Theory Difference_Bound_Matrices.DBM_Basics

theory DBM_Basics
  imports 
    DBM 
    Paths_Cycles 
    Zones
begin

subsection ‹Useful definitions›

fun get_const where
  "get_const (Le c) = c" |
  "get_const (Lt c) = c" |
  "get_const (∞ :: _ DBMEntry) = undefined"


subsection ‹Updating DBMs›

abbreviation DBM_update :: "('t::time) DBM ⇒ nat ⇒ nat ⇒ ('t DBMEntry) ⇒ ('t::time) DBM"
where
  "DBM_update M m n v ≡ (λ x y. if m = x ∧ n = y then v else M x y)"

fun DBM_upd :: "('t::time) DBM ⇒ (nat ⇒ nat ⇒ 't DBMEntry) ⇒ nat ⇒ nat ⇒ nat ⇒ 't DBM"
where
  "DBM_upd M f 0 0 _ = DBM_update M 0 0 (f 0 0)" |
  "DBM_upd M f (Suc i) 0 n = DBM_update (DBM_upd M f i n n) (Suc i) 0 (f (Suc i) 0)" |
  "DBM_upd M f i (Suc j) n = DBM_update (DBM_upd M f i j n) i (Suc j) (f i (Suc j))"

lemma upd_1:
assumes "j ≤ n"
shows "DBM_upd M1 f (Suc m) n N (Suc m) j = DBM_upd M1 f (Suc m) j N (Suc m) j"
using assms
by (induction n) auto

lemma upd_2:
assumes "i ≤ m"
shows "DBM_upd M1 f (Suc m) n N i j = DBM_upd M1 f (Suc m) 0 N i j"
using assms
proof (induction n)
  case 0 thus ?case by blast
next
  case (Suc n)
  thus ?case by simp
qed

lemma upd_3:
assumes "m ≤ N" "n ≤ N" "j ≤ n" "i ≤ m"
shows "(DBM_upd M1 f m n N) i j = (DBM_upd M1 f i j N) i j"
using assms
proof (induction m arbitrary: n i j, goal_cases)
  case (1 n) thus ?case by (induction n) auto
next
  case (2 m n i j) thus ?case
  proof (cases "i = Suc m")
    case True thus ?thesis using upd_1[OF ‹j ≤ n›] by blast
    next
    case False
    with ‹i ≤ Suc m› have "i ≤ m" by auto
    with upd_2[OF this] have "DBM_upd M1 f (Suc m) n N i j = DBM_upd M1 f m N N i j" by force
    also have "… = DBM_upd M1 f i j N i j" using False 2 by force
    finally show ?thesis .
  qed
qed

lemma upd_id:
  assumes "m ≤ N" "n ≤ N" "i ≤ m" "j ≤ n"
  shows "(DBM_upd M1 f m n N) i j = f i j"
proof -
  from assms upd_3 have "DBM_upd M1 f m n N i j = DBM_upd M1 f i j N i j" by blast
  also have "… = f i j" by (cases i; cases j; fastforce)
  finally show ?thesis .
qed


subsection ‹DBMs Without Negative Cycles are Non-Empty›

text ‹
  We need all of these assumptions for the proof that matrices without negative cycles
  represent non-negative zones:
    ▪ Abelian (linearly ordered) monoid
    ▪ Time is non-trivial
    ▪ Time is dense
›
lemmas (in linordered_ab_monoid_add) comm = add.commute

lemma sum_gt_neutral_dest':
  "(a :: (('a :: time) DBMEntry)) ≥ 0 ⟹ a + b > 0 ⟹ ∃ d. Le d ≤ a ∧ Le (-d) ≤ b ∧ d ≥ 0"
proof -
  assume "a + b > 0" "a ≥ 0"
  show ?thesis
  proof (cases "b ≥ 0")
    case True
    with ‹a ≥ 0› show ?thesis by (auto simp: neutral)
  next
    case False
    hence "b < Le 0" by (auto simp: neutral)
    note * = this ‹a ≥ 0› ‹a + b > 0›
    note [simp] = neutral
    show ?thesis
    proof (cases a, cases b, goal_cases)
      case (1 a' b')
      with * have "a' + b' > 0" by (auto elim: dbm_lt.cases simp: less add)
      hence "b' > -a'" by (metis add.commute diff_0 diff_less_eq)
      with * 1 show ?case
        by (auto simp: dbm_le_def less_eq le_dbm_le)
    next
      case (2 a' b')
      with * have "a' + b' > 0" by (auto elim: dbm_lt.cases simp: less add)
      hence "b' > -a'" by (metis add.commute diff_0 diff_less_eq)
      with * 2 show ?case
        by (auto simp: dbm_le_def less_eq le_dbm_le)
    next
      case (3 a')
      with * show ?case
        by auto
    next
      case (4 a')
      thus ?case
      proof (cases b, goal_cases)
        case (1 b')
        have "b' < 0" using 1(2) * by (metis dbm_lt.intros(3) less less_asym neqE)
        from 1 * have "a' + b' > 0" by (auto elim: dbm_lt.cases simp: less add)
        then have "-b' < a'" by (metis diff_0 diff_less_eq)
        with ‹b' < 0› * 1 show ?case by (auto simp: dbm_le_def less_eq)
      next
        case (2 b')
        with * have A: "b' ≤ 0" "a' > 0" by (auto elim: dbm_lt.cases simp: less less_eq dbm_le_def)
        show ?case
        proof (cases "b' = 0")
          case True
          from dense[OF A(2)] obtain d where d: "d > 0" "d < a'" by auto
          then have "Le (-d) < Lt b'" "Le d < Lt a'" unfolding less using True by auto
          with d(1) 2 * show ?thesis by - (rule exI[where x = "d"], auto)
        next
          case False
          with A(1) have **: "- b' > 0" by simp
          from 2 * have "a' + b' > 0" by (auto elim: dbm_lt.cases simp: less add)
          then have "-b' < a'" by (metis less_add_same_cancel1 minus_add_cancel minus_less_iff)
          from dense[OF this] obtain d where d:
            "d > -b'" "-d < b'" "d < a'"
            by (auto simp add: minus_less_iff)
          then have "Le (-d) < Lt b'" "Le d < Lt a'" unfolding less by auto
          with d(1) 2 ** show ?thesis
            by - (rule exI[where x = "d"], auto,
                  meson d(2) dual_order.order_iff_strict less_trans neg_le_0_iff_le)
        qed
      next
        case 3
        with * show ?case
          by auto
    qed
    next
      case 5 thus ?case
      proof (cases b, goal_cases)
        case (1 b')
        with * have "-b' ≥ 0"
          by (metis dbm_lt.intros(3) leI less less_asym neg_less_0_iff_less)
        let ?d = "- b'"
        have "Le ?d ≤ ∞" "Le (- ?d) ≤ Le b'" by (auto simp: any_le_inf)
        with ‹-b' ≥ 0› * 1 show ?case by auto
      next
        case (2 b')
        with * have "b' ≤ 0" by (auto elim: dbm_lt.cases simp: less)
        from non_trivial_neg obtain e :: 'a where e:"e < 0" by blast
        let ?d = "- (b' + e)"
        from e ‹b' ≤ 0› have "Le ?d ≤ ∞" "Le (- ?d) ≤ Lt b'" "b' + e < 0"
          by (auto simp: dbm_lt.intros(4) less less_imp_le any_le_inf add_nonpos_neg)
        then have "Le ?d ≤ ∞" "Le (- ?d) ≤ Lt b'" "?d ≥ 0"
          using less_imp_le neg_0_le_iff_le by blast+
        with * 2 show ?case by auto
      next
        case 3
        with * show ?case
          by auto
      qed
    qed
  qed
qed

lemma sum_gt_neutral_dest:
  "(a :: (('a :: time) DBMEntry)) + b > 0 ⟹ ∃ d. Le d ≤ a ∧ Le (-d) ≤ b"
proof -
  assume A: "a + b > 0"
  then have A': "b + a > 0" by (simp add: comm)
  show ?thesis
  proof (cases "a ≥ 0")
    case True
    with A sum_gt_neutral_dest' show ?thesis by auto
  next
    case False
    { assume "b ≤ 0"
      with False have "a ≤ 0" "b ≤ 0" by auto
      from add_mono[OF this] have "a + b ≤ 0" by auto
      with A have False by auto
    }
    then have "b ≥ 0" by fastforce
    with sum_gt_neutral_dest'[OF this A'] show ?thesis by auto
  qed
qed

subsection ‹Negative Cycles in DBMs›

lemma DBM_val_bounded_neg_cycle1:
fixes i xs assumes
  bounded: "DBM_val_bounded v u M n" and A:"i ≤ n" "set xs ⊆ {0..n}" "len M i i xs < 0" and
  surj_on: "∀ k ≤ n. k > 0 ⟶ (∃ c. v c = k)" and at_most: "i ≠ 0" "cnt 0 xs ≤ 1"
shows False
proof -
  from A(1) surj_on at_most obtain c where c: "v c = i" by auto
  with DBM_val_bounded_len'3[OF bounded at_most(2), of c c] A(1,2) surj_on
  have bounded:"dbm_entry_val u (Some c) (Some c) (len M i i xs)" by force
  from A(3) have "len M i i xs ≺ Le 0" by (simp add: neutral less)
  then show False using bounded by (cases rule: dbm_lt.cases) (auto elim: dbm_entry_val.cases)
qed

lemma cnt_0_I:
  "x ∉ set xs ⟹ cnt x xs = 0"
by (induction xs) auto

lemma distinct_cnt: "distinct xs ⟹ cnt x xs ≤ 1"
  apply (induction xs)
   apply simp
  subgoal for a xs
    using cnt_0_I by (cases "x = a") fastforce+
  done

lemma DBM_val_bounded_neg_cycle:
fixes i xs assumes
  bounded: "DBM_val_bounded v u M n" and A:"i ≤ n" "set xs ⊆ {0..n}" "len M i i xs < 0" and
  surj_on: "∀ k ≤ n. k > 0 ⟶ (∃ c. v c = k)"
shows False
proof -
  from negative_len_shortest[OF _ A(3)] obtain j ys where ys:
    "distinct (j # ys)" "len M j j ys < 0" "j ∈ set (i # xs)" "set ys ⊆ set xs"
  by blast
  show False
  proof (cases "ys = []")
    case True
    show ?thesis
    proof (cases "j = 0")
      case True
      with ‹ys = []› ys bounded show False unfolding DBM_val_bounded_def neutral less_eq[symmetric]
      by auto
    next
      case False
      with ‹ys = []› DBM_val_bounded_neg_cycle1[OF bounded _ _ ys(2) surj_on] ys(3) A(1,2)
      show False by auto
    qed
  next
    case False
    from distinct_arcs_ex[OF _ _ this, of j 0 j] ys(1) obtain a b where arc:
      "a ≠ 0" "(a, b) ∈ set (arcs j j ys)"
    by auto
    from cycle_rotate_2'[OF False this(2)] obtain zs where zs:
      "len M j j ys = len M a a (b # zs)" "set (a # b # zs) = set (j # ys)"
      "1 + length zs = length ys" "set (arcs j j ys) = set (arcs a a (b # zs))"
    by blast
    with distinct_card[OF ys(1)] have "distinct (a # b # zs)" by (intro card_distinct) auto
    with distinct_cnt[of "b # zs"] have *: "cnt 0 (b # zs) ≤ 1" by fastforce
    show ?thesis
     apply (rule DBM_val_bounded_neg_cycle1[OF bounded _ _ _ surj_on ‹a ≠ 0› *])
       using zs(2) ys(3,4) A(1,2) apply fastforce+
    using zs(1) ys(2) by simp
  qed
qed

paragraph ‹Nicer Path Boundedness Theorems›

lemma DBM_val_bounded_len_1:
  fixes v
  assumes "DBM_val_bounded v u M n" "v c ≤ n" "set vs ⊆ {0..n}" "∀ k ≤ n. (∃ c. v c = k)"
  shows "dbm_entry_val u (Some c) None (len M (v c) 0 vs)" using assms
proof (induction "length vs" arbitrary: vs rule: less_induct)
  case A: less
  show ?case
  proof (cases "0 ∈ set vs")
    case False
    with DBM_val_bounded_len_1'_aux[OF A(2,3)] A(4,5) show ?thesis by fastforce
  next
    case True
    then obtain xs ys where vs: "vs = xs @ 0 # ys" by (meson split_list)
    from len_decomp[OF this] have "len M (v c) 0 vs = len M (v c) 0 xs + len M 0 0 ys" .
    moreover have "len M 0 0 ys ≥ 0"
    proof (rule ccontr, goal_cases)
      case 1
      then have "len M 0 0 ys < 0" by simp
      with DBM_val_bounded_neg_cycle[OF assms(1), of 0 ys] vs A(4,5) show False by auto
    qed
    ultimately have *: "len M (v c) 0 vs ≥ len M (v c) 0 xs" by (simp add: add_increasing2)
    from vs A have "dbm_entry_val u (Some c) None (len M (v c) 0 xs)" by auto
    from dbm_entry_val_mono3[OF this, of "len M (v c) 0 vs"] * show ?thesis unfolding less_eq by auto
  qed
qed

lemma DBM_val_bounded_len_2:
  fixes v
  assumes "DBM_val_bounded v u M n" "v c ≤ n" "set vs ⊆ {0..n}" "∀ k ≤ n. (∃ c. v c = k)"
  shows "dbm_entry_val u None (Some c) (len M 0 (v c) vs)" using assms
proof (induction "length vs" arbitrary: vs rule: less_induct)
  case A: less
  show ?case
  proof (cases "0 ∈ set vs")
    case False
    with DBM_val_bounded_len_2'_aux[OF A(2,3)] A(4,5) show ?thesis by fastforce
  next
    case True
    then obtain xs ys where vs: "vs = xs @ 0 # ys" by (meson split_list)
    from len_decomp[OF this] have "len M 0 (v c) vs = len M 0 0 xs + len M 0 (v c) ys" .
    moreover have "len M 0 0 xs ≥ 0"
    proof (rule ccontr, goal_cases)
      case 1
      then have "len M 0 0 xs < 0" by simp
      with DBM_val_bounded_neg_cycle[OF assms(1), of 0 xs] vs A(4,5) show False by auto
    qed
    ultimately have *: "len M 0 (v c) vs ≥ len M 0 (v c) ys" by (simp add: add_increasing)
    from vs A have "dbm_entry_val u None (Some c) (len M 0 (v c) ys)" by auto
    from dbm_entry_val_mono2[OF this] * show ?thesis unfolding less_eq by auto
  qed
qed

lemma DBM_val_bounded_len_3:
  fixes v
  assumes "DBM_val_bounded v u M n" "v c1 ≤ n" "v c2 ≤ n" "set vs ⊆ {0..n}"
          "∀ k ≤ n. (∃ c. v c = k)"
  shows "dbm_entry_val u (Some c1) (Some c2) (len M (v c1) (v c2) vs)" using assms
proof (cases "0 ∈ set vs")
  case False
  with DBM_val_bounded_len_3'_aux[OF assms(1-3)] assms(4-) show ?thesis by fastforce
next
  case True
  then obtain xs ys where vs: "vs = xs @ 0 # ys" by (meson split_list)
  from assms(4,5) vs DBM_val_bounded_len_1[OF assms(1,2)] DBM_val_bounded_len_2[OF assms(1,3)]
  have
    "dbm_entry_val u (Some c1) None (len M (v c1) 0 xs)"
    "dbm_entry_val u None (Some c2) (len M 0 (v c2) ys)"
  by auto
  from dbm_entry_val_add_4[OF this] len_decomp[OF vs, of M] show ?thesis unfolding add by auto
qed

text ‹An equivalent way of handling ‹𝟬››

fun val_0 :: "('c ⇒ ('a :: linordered_ab_group_add)) ⇒ 'c option ⇒ 'a" where
  "val_0 u None = 0" |
  "val_0 u (Some c) = u c"

notation val_0 (‹_⇩𝟬 _› [90,90] 90)

lemma dbm_entry_val_None_None[dest]:
  "dbm_entry_val u None None l ⟹ l = ∞"
by (auto elim: dbm_entry_val.cases)

lemma dbm_entry_val_dbm_lt:
  assumes "dbm_entry_val u x y l"
  shows "Lt (u⇩𝟬 x - u⇩𝟬 y) ≺ l"
using assms by (cases rule: dbm_entry_val.cases, auto)

lemma dbm_lt_dbm_entry_val_1:
  assumes "Lt (u x) ≺ l"
  shows "dbm_entry_val u (Some x) None l"
using assms by (cases rule: dbm_lt.cases) auto

lemma dbm_lt_dbm_entry_val_2:
  assumes "Lt (- u x) ≺ l"
  shows "dbm_entry_val u None (Some x) l"
using assms by (cases rule: dbm_lt.cases) auto

lemma dbm_lt_dbm_entry_val_3:
  assumes "Lt (u x - u y) ≺ l"
  shows "dbm_entry_val u (Some x) (Some y) l"
using assms by (cases rule: dbm_lt.cases) auto

text ‹A more uniform theorem for boundedness by paths›

lemma DBM_val_bounded_len:
  fixes v
  defines "v' ≡ λ x. if x = None then 0 else v (the x)"
  assumes "DBM_val_bounded v u M n" "v' x ≤ n" "v' y ≤ n" "set vs ⊆ {0..n}"
          "∀ k ≤ n. (∃ c. v c = k)" "x ≠ None ∨ y ≠ None"
  shows "Lt (u⇩𝟬 x - u⇩𝟬 y) ≺ len M (v' x) (v' y) vs" using assms
apply -
apply (rule dbm_entry_val_dbm_lt)
apply (cases x; cases y)
   apply simp_all
  apply (rule DBM_val_bounded_len_2; auto)
 apply (rule DBM_val_bounded_len_1; auto)
apply (rule DBM_val_bounded_len_3; auto)
done

subsection ‹Floyd-Warshall Algorithm Preservers Zones›

lemma D_dest: "x = D m i j k ⟹
  x ∈ {len m i j xs |xs. set xs ⊆ {0..k} ∧ i ∉ set xs ∧ j ∉ set xs ∧ distinct xs}"
using Min_elem_dest[OF D_base_finite'' D_base_not_empty] by (fastforce simp add: D_def)

lemma FW_zone_equiv:
  "∀ k ≤ n. k > 0 ⟶ (∃ c. v c = k) ⟹ [M]⇘v,n⇙ = [FW M n]⇘v,n⇙"
proof safe
  fix u assume A: "u ∈ [FW M n]⇘v,n⇙"
  { fix i j assume "i ≤ n" "j ≤ n"
    hence "FW M n i j ≤ M i j" using fw_mono[of i n j M] by simp
    hence "FW M n i j ≼ M i j" by (simp add: less_eq)
  }
  with DBM_le_subset[of n "FW M n" M] A show "u ∈ [M]⇘v,n⇙" by auto
next
  fix u assume u:"u ∈ [M]⇘v,n⇙" and surj_on: "∀ k ≤ n. k > 0 ⟶ (∃ c. v c = k)"
  hence *:"DBM_val_bounded v u M n" by (simp add: DBM_zone_repr_def)
  note ** = DBM_val_bounded_neg_cycle[OF this _ _ _ surj_on]
  have cyc_free: "cyc_free M n" using ** by fastforce
  from cyc_free_diag[OF this] have diag_ge_zero: "∀k≤n. M k k ≥ Le 0" unfolding neutral by auto

  have "DBM_val_bounded v u (FW M n) n" unfolding DBM_val_bounded_def
  proof (safe, goal_cases)
    case 1
    from fw_shortest_path[OF cyc_free] have **:
      "D M 0 0 n = FW M n 0 0"
    by (simp add: neutral)
    from D_dest[OF **[symmetric]] obtain xs where xs:
        "FW M n 0 0 = len M 0 0 xs" "set xs ⊆ {0..n}"
        "0 ∉ set xs" "distinct xs"
    by auto
    with cyc_free have "FW M n 0 0 ≥ 0" by auto
    then show ?case unfolding neutral less_eq by simp
  next
    case (2 c)
    with fw_shortest_path[OF cyc_free] have **:
      "D M 0 (v c) n = FW M n 0 (v c)"
    by (simp add: neutral)
    from D_dest[OF **[symmetric]] obtain xs where xs:
        "FW M n 0 (v c) = len M 0 (v c) xs" "set xs ⊆ {0..n}"
        "0 ∉ set xs" "v c ∉ set xs" "distinct xs"
    by auto
    show ?case unfolding xs(1) using xs surj_on ‹v c ≤ n›
    by - (rule DBM_val_bounded_len'2[OF * xs(3)]; auto)
  next
    case (3 c)
    with fw_shortest_path[OF cyc_free] have **:
      "D M (v c) 0 n = FW M n (v c) 0"
    by (simp add: neutral)
    with D_dest[OF **[symmetric]] obtain xs where xs:
      "FW M n (v c) 0 = len M (v c) 0 xs" "set xs ⊆ {0..n}"
      "0 ∉ set xs" "v c ∉ set xs" "distinct xs"
    by auto
    show ?case unfolding xs(1) using xs surj_on ‹v c ≤ n›
    by - (rule DBM_val_bounded_len'1[OF * xs(3)]; auto)
  next
    case (4 c1 c2)
    with fw_shortest_path[OF cyc_free]
    have "D M (v c1) (v c2) n = FW M n (v c1) (v c2)" by (simp add: neutral)
    from D_dest[OF this[symmetric]] obtain xs where xs:
      "FW M n (v c1) (v c2) = len M (v c1) (v c2) xs" "set xs ⊆ {0..n}"
      "v c1 ∉ set xs" "v c2 ∉ set xs" "distinct xs"
    by auto
    show ?case
      unfolding xs(1)
      apply (rule DBM_val_bounded_len'3[OF *])
      using xs surj_on ‹v c1 ≤ n› ‹v c2 ≤ n› by (auto dest!: distinct_cnt[of _ 0])
  qed
  then show "u ∈ [FW M n]⇘v,n⇙" unfolding DBM_zone_repr_def by simp
qed

lemma new_negative_cycle_aux':
  fixes M :: "('a :: time) DBM"
  fixes i j d
  defines "M' ≡ λ i' j'. if (i' = i ∧ j' = j) then Le d
                       else if (i' = j ∧ j' = i) then Le (-d)
                       else M i' j'"
  assumes "i ≤ n" "j ≤ n" "set xs ⊆ {0..n}" "cycle_free M n" "length xs = m"
  assumes "len M' i i (j # xs) < 0 ∨ len M' j j (i # xs) < 0"
  assumes "i ≠ j"
  shows "∃xs. set xs ⊆ {0..n} ∧ j ∉ set xs ∧ i ∉ set xs
              ∧ (len M' i i (j # xs) < 0 ∨ len M' j j (i # xs) < 0)" using assms
proof (induction _ m arbitrary: xs rule: less_induct)
  case (less x)
  { fix b a xs assume A: "(i, j) ∉ set (arcs b a xs)" "(j, i) ∉ set (arcs b a xs)"
    with ‹i ≠ j› have "len M' b a xs = len M b a xs"
    unfolding M'_def by (induction xs arbitrary: b) auto
  } note * = this
  { fix a xs assume A:"(i, j) ∉ set (arcs a a xs)" "(j, i) ∉ set (arcs a a xs)"
    assume a: "a ≤ n" and xs: "set xs ⊆ {0..n}" and cycle: "¬ len M' a a xs ≥ 0"
    from *[OF A] have "len M' a a xs = len M a a xs" .
    with ‹cycle_free M n› ‹i ≤ n› cycle xs a have False unfolding cycle_free_def by auto
  } note ** = this
  { fix a :: nat fix ys :: "nat list"
    assume A: "ys ≠ []" "length ys ≤ length xs" "set ys ⊆ set xs" "a ≤ n"
    assume cycle: "len M' a a ys < 0"
    assume arcs: "(i, j) ∈ set (arcs a a ys) ∨ (j, i) ∈ set (arcs a a ys)"
    from arcs have ?thesis
    proof
      assume "(i, j) ∈ set (arcs a a ys)"
      from cycle_rotate_2[OF ‹ys ≠ []› this, of M']
      obtain ws where ws: "len M' a a ys = len M' i i (j # ws)" "set ws ⊆ set (a # ys)"
        "length ws < length ys" by auto
      with cycle less.hyps(1)[OF _ less.hyps(2) , of "length ws" ws] less.prems A
      show ?thesis by fastforce
    next
      assume "(j, i) ∈ set (arcs a a ys)"
      from cycle_rotate_2[OF ‹ys ≠ []› this, of M']
      obtain ws where ws: "len M' a a ys = len M' j j (i # ws)" "set ws ⊆ set (a # ys)"
        "length ws < length ys" by auto
      with cycle less.hyps(1)[OF _ less.hyps(2) , of "length ws" ws] less.prems A
      show ?thesis by fastforce
    qed
  } note *** = this
  { fix a :: nat fix ys :: "nat list"
    assume A: "ys ≠ []" "length ys ≤ length xs" "set ys ⊆ set xs" "a ≤ n"
    assume cycle: "¬ len M' a a ys ≥ 0"
    with A **[of a ys] less.prems
    have "(i, j) ∈ set (arcs a a ys) ∨ (j, i) ∈ set (arcs a a ys)" by auto
    with ***[OF A] cycle have ?thesis by auto
  } note neg_cycle_IH = this
  from cycle_free_diag[OF ‹cycle_free M n›] have "∀i. i ≤ n ⟶ Le 0 ≤ M i i" unfolding neutral by auto
  then have M'_diag: "∀i. i ≤ n ⟶ Le 0 ≤ M' i i" unfolding M'_def using ‹i ≠ j› by auto
  from less(8) show ?thesis
  proof standard
    assume cycle:"len M' i i (j # xs) < 0"
    show ?thesis
    proof (cases "i ∈ set xs")
      case False
      then show ?thesis
      proof (cases "j ∈ set xs")
        case False
        with ‹i ∉ set xs› show ?thesis using less.prems(3,6) by auto
      next
        case True
        then obtain ys zs where ys_zs: "xs = ys @ j # zs" by (meson split_list)
        with len_decomp[of "j # xs" "j # ys" j zs M' i i]
        have len: "len M' i i (j # xs) = M' i j + len M' j j ys + len M' j i zs" by auto
        show ?thesis
        proof (cases "len M' j j ys ≥ 0")
          case True
          have "len M' i i (j # zs) = M' i j + len M' j i zs" by simp
          also from len True have "M' i j + len M' j i zs ≤ len M' i i (j # xs)"
          by (metis add_le_impl add_lt_neutral comm not_le)
          finally have cycle': "len M' i i (j # zs) < 0" using cycle by auto
          from ys_zs less.prems(5) have "x > length zs" by auto
          from cycle' less.prems ys_zs less.hyps(1)[OF this less.hyps(2) , of zs]
          show ?thesis by auto
        next
          case False
          with M'_diag less.prems have "ys ≠ []" by (auto simp: neutral)
          from neg_cycle_IH[OF this] ys_zs False less.prems(1,2) show ?thesis by auto
        qed
      qed
    next
      case True
      then obtain ys zs where ys_zs: "xs = ys @ i # zs" by (meson split_list)
      with len_decomp[of "j # xs" "j # ys" i zs M' i i]
      have len: "len M' i i (j # xs) = M' i j + len M' j i ys + len M' i i zs" by auto
      show ?thesis
      proof (cases "len M' i i zs ≥ 0")
        case True
        have "len M' i i (j # ys) = M' i j + len M' j i ys" by simp
        also from len True have "M' i j + len M' j i ys ≤ len M' i i (j # xs)"
        by (metis add_lt_neutral comm not_le)
        finally have cycle': "len M' i i (j # ys) < 0" using cycle by auto
        from ys_zs less.prems(5) have "x > length ys" by auto
        from cycle' less.prems ys_zs less.hyps(1)[OF this less.hyps(2) , of ys]
        show ?thesis by auto
      next
        case False
        with less.prems(1,7) M'_diag have "zs ≠ []" by (auto simp: neutral)
        from neg_cycle_IH[OF this] ys_zs False less.prems(1,2) show ?thesis by auto
      qed
    qed
  next
    assume cycle:"len M' j j (i # xs) < 0"
    show ?thesis
    proof (cases "j ∈ set xs")
      case False
      then show ?thesis
      proof (cases "i ∈ set xs")
        case False
        with ‹j ∉ set xs› show ?thesis using less.prems(3,6) by auto
      next
        case True
        then obtain ys zs where ys_zs: "xs = ys @ i # zs" by (meson split_list)
        with len_decomp[of "i # xs" "i # ys" i zs M' j j]
        have len: "len M' j j (i # xs) = M' j i + len M' i i ys + len M' i j zs" by auto
        show ?thesis
        proof (cases "len M' i i ys ≥ 0")
          case True
          have "len M' j j (i # zs) = M' j i + len M' i j zs" by simp
          also from len True have "M' j i + len M' i j zs ≤ len M' j j (i # xs)"
          by (metis add_le_impl add_lt_neutral comm not_le)
          finally have cycle': "len M' j j (i # zs) < 0" using cycle by auto
          from ys_zs less.prems(5) have "x > length zs" by auto
          from cycle' less.prems ys_zs less.hyps(1)[OF this less.hyps(2) , of zs]
          show ?thesis by auto
        next
          case False
          with less.prems M'_diag have "ys ≠ []" by (auto simp: neutral)
          from neg_cycle_IH[OF this] ys_zs False less.prems(1,2) show ?thesis by auto
        qed
      qed
    next
      case True
      then obtain ys zs where ys_zs: "xs = ys @ j # zs" by (meson split_list)
      with len_decomp[of "i # xs" "i # ys" j zs M' j j]
      have len: "len M' j j (i # xs) = M' j i + len M' i j ys + len M' j j zs" by auto
      show ?thesis
      proof (cases "len M' j j zs ≥ 0")
        case True
        have "len M' j j (i # ys) = M' j i + len M' i j ys" by simp
        also from len True have "M' j i + len M' i j ys ≤ len M' j j (i # xs)"
        by (metis add_lt_neutral comm not_le)
        finally have cycle': "len M' j j (i # ys) < 0" using cycle by auto
        from ys_zs less.prems(5) have "x > length ys" by auto
        from cycle' less.prems ys_zs less.hyps(1)[OF this less.hyps(2) , of ys]
        show ?thesis by auto
      next
        case False
        with less.prems(2,7) M'_diag have "zs ≠ []" by (auto simp: neutral)
        from neg_cycle_IH[OF this] ys_zs False less.prems(1,2) show ?thesis by auto
      qed
    qed
  qed
qed

lemma new_negative_cycle_aux:
  fixes M :: "('a :: time) DBM"
  fixes i d
  defines "M' ≡ λ i' j'. if (i' = i ∧ j' = 0) then Le d
                       else if (i' = 0 ∧ j' = i) then Le (-d)
                       else M i' j'"
  assumes "i ≤ n" "set xs ⊆ {0..n}" "cycle_free M n" "length xs = m"
  assumes "len M' 0 0 (i # xs) < 0 ∨ len M' i i (0 # xs) < 0"
  assumes "i ≠ 0"
  shows "∃xs. set xs ⊆ {0..n} ∧ 0 ∉ set xs ∧ i ∉ set xs
              ∧ (len M' 0 0 (i # xs) < 0 ∨ len M' i i (0 # xs) < 0)" using assms
proof (induction _ m arbitrary: xs rule: less_induct)
  case (less x)
  { fix b a xs assume A: "(0, i) ∉ set (arcs b a xs)" "(i, 0) ∉ set (arcs b a xs)"
    then have "len M' b a xs = len M b a xs"
    unfolding M'_def by (induction xs arbitrary: b) auto
  } note * = this
  { fix a xs assume A:"(0, i) ∉ set (arcs a a xs)" "(i, 0) ∉ set (arcs a a xs)"
    assume a: "a ≤ n" and xs: "set xs ⊆ {0..n}" and cycle: "¬ len M' a a xs ≥ 0"
    from *[OF A] have "len M' a a xs = len M a a xs" .
    with ‹cycle_free M n› ‹i ≤ n› cycle xs a have False unfolding cycle_free_def by auto
  } note ** = this
  { fix a :: nat fix ys :: "nat list"
    assume A: "ys ≠ []" "length ys ≤ length xs" "set ys ⊆ set xs" "a ≤ n"
    assume cycle: "len M' a a ys < 0"
    assume arcs: "(0, i) ∈ set (arcs a a ys) ∨ (i, 0) ∈ set (arcs a a ys)"
    from arcs have ?thesis
    proof
      assume "(0, i) ∈ set (arcs a a ys)"
      from cycle_rotate_2[OF ‹ys ≠ []› this, of M']
      obtain ws where ws: "len M' a a ys = len M' 0 0 (i # ws)" "set ws ⊆ set (a # ys)"
        "length ws < length ys" by auto
      with cycle less.hyps(1)[OF _ less.hyps(2) , of "length ws" ws] less.prems A
      show ?thesis by fastforce
    next
      assume "(i, 0) ∈ set (arcs a a ys)"
      from cycle_rotate_2[OF ‹ys ≠ []› this, of M']
      obtain ws where ws: "len M' a a ys = len M' i i (0 # ws)" "set ws ⊆ set (a # ys)"
        "length ws < length ys" by auto
      with cycle less.hyps(1)[OF _ less.hyps(2) , of "length ws" ws] less.prems A
      show ?thesis by fastforce
    qed
  } note *** = this
  { fix a :: nat fix ys :: "nat list"
    assume A: "ys ≠ []" "length ys ≤ length xs" "set ys ⊆ set xs" "a ≤ n"
    assume cycle: "¬ len M' a a ys ≥ 0"
    with A **[of a ys]  less.prems(2)
    have "(0, i) ∈ set (arcs a a ys) ∨ (i, 0) ∈ set (arcs a a ys)" by auto
    with ***[OF A] cycle have ?thesis by auto
  } note neg_cycle_IH = this
  from cycle_free_diag[OF ‹cycle_free M n›] have "∀i. i ≤ n ⟶ Le 0 ≤ M i i" unfolding neutral by auto
  then have M'_diag: "∀i. i ≤ n ⟶ Le 0 ≤ M' i i" unfolding M'_def using ‹i ≠ 0› by auto
  from less(7) show ?thesis
  proof standard
    assume cycle:"len M' 0 0 (i # xs) < 0"
    show ?thesis
    proof (cases "0 ∈ set xs")
      case False
      thus ?thesis
      proof (cases "i ∈ set xs")
        case False
        with ‹0 ∉ set xs› show ?thesis using less.prems by auto
      next
        case True
        then obtain ys zs where ys_zs: "xs = ys @ i # zs" by (meson split_list)
        with len_decomp[of "i # xs" "i # ys" i zs M' 0 0]
        have len: "len M' 0 0 (i # xs) = M' 0 i + len M' i i ys + len M' i 0 zs" by auto
        show ?thesis
        proof (cases "len M' i i ys ≥ 0")
          case True
          have "len M' 0 0 (i # zs) = M' 0 i + len M' i 0 zs" by simp
          also from len True have "M' 0 i + len M' i 0 zs ≤ len M' 0 0 (i # xs)"
          by (metis add_le_impl add_lt_neutral comm not_le)
          finally have cycle': "len M' 0 0 (i # zs) < 0" using cycle by auto
          from ys_zs less.prems(4) have "x > length zs" by auto
          from cycle' less.prems ys_zs less.hyps(1)[OF this less.hyps(2) , of zs]
          show ?thesis by auto
        next
          case False
          with less.prems(1,6) M'_diag have "ys ≠ []" by (auto simp: neutral)
          from neg_cycle_IH[OF this] ys_zs False less.prems(1,2) show ?thesis by auto
        qed
      qed
    next
      case True
      then obtain ys zs where ys_zs: "xs = ys @ 0 # zs" by (meson split_list)
      with len_decomp[of "i # xs" "i # ys" 0 zs M' 0 0]
      have len: "len M' 0 0 (i # xs) = M' 0 i + len M' i 0 ys + len M' 0 0 zs" by auto
      show ?thesis
      proof (cases "len M' 0 0 zs ≥ 0")
        case True
        have "len M' 0 0 (i # ys) = M' 0 i + len M' i 0 ys" by simp
        also from len True have "M' 0 i + len M' i 0 ys ≤ len M' 0 0 (i # xs)"
        by (metis add_lt_neutral comm not_le)
        finally have cycle': "len M' 0 0 (i # ys) < 0" using cycle by auto
        from ys_zs less.prems(4) have "x > length ys" by auto
        from cycle' less.prems ys_zs less.hyps(1)[OF this less.hyps(2) , of ys]
        show ?thesis by auto
      next
        case False
        with less.prems(1,6) M'_diag have "zs ≠ []" by (auto simp: neutral)
        from neg_cycle_IH[OF this] ys_zs False less.prems(1,2) show ?thesis by auto
      qed
    qed
  next
    assume cycle: "len M' i i (0 # xs) < 0"
    show ?thesis
    proof (cases "i ∈ set xs")
      case False
      thus ?thesis
      proof (cases "0 ∈ set xs")
        case False
        with ‹i ∉ set xs› show ?thesis using less.prems by auto
      next
        case True
        then obtain ys zs where ys_zs: "xs = ys @ 0 # zs" by (meson split_list)
        with len_decomp[of "0 # xs" "0 # ys" 0 zs M' i i]
        have len: "len M' i i (0 # xs) = M' i 0 + len M' 0 0 ys + len M' 0 i zs" by auto
        show ?thesis
        proof (cases "len M' 0 0 ys ≥ 0")
          case True
          have "len M' i i (0 # zs) = M' i 0 + len M' 0 i zs" by simp
          also from len True have "M' i 0 + len M' 0 i zs ≤ len M' i i (0 # xs)"
          by (metis add_le_impl add_lt_neutral comm not_le)
          finally have cycle': "len M' i i (0 # zs) < 0" using cycle by auto
          from ys_zs less.prems(4) have "x > length zs" by auto
          from cycle' less.prems ys_zs less.hyps(1)[OF this less.hyps(2) , of zs]
          show ?thesis by auto
        next
          case False
          with less.prems(1,6) M'_diag have "ys ≠ []" by (auto simp: neutral)
          from neg_cycle_IH[OF this] ys_zs False less.prems(1,2) show ?thesis by auto
        qed
      qed
    next
      case True
      then obtain ys zs where ys_zs: "xs = ys @ i # zs" by (meson split_list)
      with len_decomp[of "0 # xs" "0 # ys" i zs M' i i]
      have len: "len M' i i (0 # xs) = M' i 0 + len M' 0 i ys + len M' i i zs" by auto
      show ?thesis
      proof (cases "len M' i i zs ≥ 0")
        case True
        have "len M' i i (0 # ys) = M' i 0 + len M' 0 i ys" by simp
        also from len True have "M' i 0 + len M' 0 i ys ≤ len M' i i (0 # xs)"
        by (metis add_lt_neutral comm not_le)
        finally have cycle': "len M' i i (0 # ys) < 0" using cycle by auto
        from ys_zs less.prems(4) have "x > length ys" by auto
        from cycle' less.prems ys_zs less.hyps(1)[OF this less.hyps(2) , of ys]
        show ?thesis by auto
      next
        case False
        with less.prems(1,6) M'_diag have "zs ≠ []" by (auto simp: neutral)
        from neg_cycle_IH[OF this] ys_zs False less.prems(1,2) show ?thesis by auto
      qed
    qed
  qed
qed


section ‹The Characteristic Property of Canonical DBMs›

theorem fix_index':
  fixes M :: "(('a :: time) DBMEntry) mat"
  assumes "Le r ≤ M i j" "Le (-r) ≤ M j i" "cycle_free M n" "canonical M n" "i ≤ n" "j ≤ n" "i ≠ j"
  defines "M' ≡ λ i' j'. if (i' = i ∧ j' = j) then Le r
                       else if (i' = j ∧ j' = i) then Le (-r)
                       else M i' j'"
  shows "(∀ u. DBM_val_bounded v u M' n ⟶ DBM_val_bounded v u M n) ∧ cycle_free M' n"
proof -
  note A = assms
  note r = assms(1,2)
  from ‹cycle_free M n› have diag_cycles: "∀i xs. i ≤ n ∧ set xs ⊆ {0..n} ⟶ Le 0 ≤ len M i i xs"
  unfolding cycle_free_def neutral by auto
  let ?M' = "λ i' j'. if (i' = i ∧ j' = j) then Le r
                       else if (i' = j ∧ j' = i) then Le (-r)
                       else M i' j'"
  have "?M' i' j' ≤ M i' j'" when "i' ≤ n" "j' ≤ n" for i' j' using assms by auto
  with DBM_le_subset[folded less_eq, of n ?M' M] have "DBM_val_bounded v u M n"
  if "DBM_val_bounded v u ?M' n" for u unfolding DBM_zone_repr_def using that by auto
  then have not_empty:"∀ u. DBM_val_bounded v u ?M' n ⟶ DBM_val_bounded v u M n" by auto
  { fix a xs assume prems: "a ≤ n" "set xs ⊆ {0..n}" and cycle: "¬ len ?M' a a xs ≥ 0"
    { fix b assume A: "(i, j) ∉ set (arcs b a xs)" "(j, i) ∉ set (arcs b a xs)"
      with ‹i ≠ j› have "len ?M' b a xs = len M b a xs" by (induction xs arbitrary: b) auto
    } note * = this
    { fix a b xs assume A: "i ∉ set (a # xs)" "j ∉ set (a # xs)"
      then have "len ?M' a b xs = len M a b xs" by (induction xs arbitrary: a, auto)
    } note ** = this
    { assume A:"(i, j) ∉ set (arcs a a xs)" "(j, i) ∉ set (arcs a a xs)"
      from *[OF this] have "len ?M' a a xs = len M a a xs" .
      with ‹cycle_free M n› prems cycle have False by (auto simp: cycle_free_def)
    }
    then have arcs:"(i, j) ∈ set (arcs a a xs) ∨ (j, i) ∈ set (arcs a a xs)" by auto
    with ‹i ≠ j› have "xs ≠ []" by auto
    from arcs obtain xs where xs: "set xs ⊆ {0..n}"
      "len ?M' i i (j # xs) < 0 ∨ len ?M' j j (i # xs) < 0"
    proof (standard, goal_cases)
      case 1
      from cycle_rotate_2'[OF ‹xs ≠ []› this(2), of ?M'] prems obtain ys where
        "len ?M' i i (j # ys) = len ?M' a a xs" "set ys ⊆ {0..n}"
      by fastforce
      with 1 cycle show ?thesis by fastforce
    next
      case 2
      from cycle_rotate_2'[OF ‹xs ≠ []› this(2), of ?M'] prems obtain ys where
        "len ?M' j j (i # ys) = len ?M' a a xs" "set ys ⊆ {0..n}"
      by fastforce
      with 2 cycle show ?thesis by fastforce
    qed
    from new_negative_cycle_aux'[OF ‹i ≤ n› ‹j ≤ n› this(1) ‹cycle_free M n› _ this(2) ‹i ≠ j›]
    obtain xs where xs:
      "set xs ⊆ {0..n}" "i ∉ set xs" "j ∉ set xs"
      "len ?M' i i (j # xs) < 0 ∨ len ?M' j j (i # xs) < 0"
    by auto
    from this(4) have False
    proof
      assume A: "len ?M' j j (i # xs) < 0"
      show False
      proof (cases xs)
        case Nil
        with ‹i ≠ j› have *:"?M' j i = Le (-r)" "?M' i j = Le r" by simp+
        from Nil have "len ?M' j j (i # xs) = ?M' j i + ?M' i j" by simp
        with * have "len ?M' j j (i # xs) = Le 0" by (simp add: add)
        then show False using A by (simp add: neutral)
      next
        case (Cons y ys)
        have *:"M i y + M y j ≥ M i j"
        using ‹canonical M n› Cons xs ‹i ≤ n› ‹j ≤ n› by (simp add: add less_eq)
        have "Le 0 = Le (-r) + Le r" by (simp add: add)
        also have "… ≤ Le (-r) + M i j" using r by (simp add: add_mono)
        also have "… ≤ Le (-r) + M i y + M y j" using * by (simp add: add_mono add.assoc)
        also have "… ≤ Le (-r) + ?M' i y + len M y j ys"
          using canonical_len[OF ‹canonical M n›] xs(1-3) ‹i ≤ n› ‹j ≤ n› Cons
          by (simp add: add_mono)
        also have "… = len ?M' j j (i # xs)" using Cons ‹i ≠ j› ** xs(1-3)
          by (simp add: add.assoc)
        also have "… < Le 0" using A by (simp add: neutral)
        finally show False by simp
      qed
    next
      assume A: "len ?M' i i (j # xs) < 0"
      show False
      proof (cases xs)
        case Nil
        with ‹i ≠ j› have *:"?M' j i = Le (-r)" "?M' i j = Le r" by simp+
        from Nil have "len ?M' i i (j # xs) = ?M' i j + ?M' j i" by simp
        with * have "len ?M' i i (j # xs) = Le 0" by (simp add: add)
        then show False using A by (simp add: neutral)
      next
        case (Cons y ys)
        have *:"M j y + M y i ≥ M j i"
        using ‹canonical M n› Cons xs ‹i ≤ n› ‹j ≤ n› by (simp add: add less_eq)
        have "Le 0 = Le r + Le (-r)" by (simp add: add)
        also have "… ≤ Le r + M j i" using r by (simp add: add_mono)
        also have "… ≤ Le r + M j y + M y i" using * by (simp add: add_mono add.assoc)
        also have "… ≤ Le r + ?M' j y + len M y i ys"
          using canonical_len[OF ‹canonical M n›] xs(1-3) ‹i ≤ n› ‹j ≤ n› Cons
          by (simp add: add_mono)
        also have "… = len ?M' i i (j # xs)" using Cons ‹i ≠ j› ** xs(1-3)
          by (simp add: add.assoc)
        also have "… < Le 0" using A by (simp add: neutral)
        finally show False by simp
      qed
    qed
  } note * = this
  have "cycle_free ?M' n" unfolding cycle_free_diag_equiv[symmetric]
    using negative_cycle_dest_diag * by fastforce
  then show ?thesis using not_empty ‹i ≠ j› r unfolding M'_def by auto
qed

lemma fix_index:
  fixes M :: "(('a :: time) DBMEntry) mat"
  assumes "M 0 i + M i 0 > 0" "cycle_free M n" "canonical M n" "i ≤ n" "i ≠ 0"
  shows
  "∃ (M' :: ('a DBMEntry) mat). ((∃ u. DBM_val_bounded v u M' n) ⟶ (∃ u. DBM_val_bounded v u M n))
     ∧ M' 0 i + M' i 0 = 0 ∧ cycle_free M' n
     ∧ (∀ j. i ≠ j ∧ M 0 j + M j 0 = 0 ⟶ M' 0 j + M' j 0 = 0)
     ∧ (∀ j. i ≠ j ∧ M 0 j + M j 0 > 0 ⟶ M' 0 j + M' j 0 > 0)"
proof -
  note A = assms
  from sum_gt_neutral_dest[OF assms(1)] obtain d where d: "Le d ≤ M i 0" "Le (-d) ≤ M 0 i" by auto
  have "i ≠ 0" using A by - (rule ccontr; simp)
  let ?M' = "λi' j'. if i' = i ∧ j' = 0 then Le d else if i' = 0 ∧ j' = i then Le (-d) else M i' j'"
  from fix_index'[OF d(1,2) A(2,3,4) _ ‹i ≠ 0›] have M':
    "∀u. DBM_val_bounded v u ?M' n ⟶ DBM_val_bounded v u M n" "cycle_free ?M' n"
  by auto
  moreover from ‹i ≠ 0› have "∀ j. i ≠ j ∧ M 0 j + M j 0 = 0 ⟶ ?M' 0 j + ?M' j 0 = 0" by auto
  moreover from ‹i ≠ 0› have "∀ j. i ≠ j ∧ M 0 j + M j 0 > 0 ⟶ ?M' 0 j + ?M' j 0 > 0" by auto
  moreover from ‹i ≠ 0› have "?M' 0 i + ?M' i 0 = 0" unfolding neutral add by auto
  ultimately show ?thesis by blast
qed

subsubsection ‹
  Putting it together
›

lemma FW_not_empty:
  "DBM_val_bounded v u (FW M' n) n ⟹ DBM_val_bounded v u M' n"
proof -
  assume A: "DBM_val_bounded v u (FW M' n) n"
  have "∀i j. i ≤ n ⟶ j ≤ n ⟶ FW M' n i j ≤ M' i j" using fw_mono by blast
  from DBM_le_subset[of n "FW M' n" M' _ v, OF this[unfolded less_eq]]
  show "DBM_val_bounded v u M' n" using A by (auto simp: DBM_zone_repr_def)
qed

lemma fix_indices:
  fixes M :: "(('a :: time) DBMEntry) mat"
  assumes "set xs ⊆ {0..n}" "distinct xs"
  assumes "cyc_free M n" "canonical M n"
  shows
  "∃ (M' :: ('a DBMEntry) mat). ((∃ u. DBM_val_bounded v u M' n) ⟶ (∃ u. DBM_val_bounded v u M n))
     ∧ (∀ i ∈ set xs. i ≠ 0 ⟶ M' 0 i + M' i 0 = 0) ∧ cyc_free M' n
     ∧ (∀ i≤n. i ∉ set xs ∧ M 0 i + M i 0 = 0 ⟶ M' 0 i + M' i 0 = 0)" using assms
proof (induction xs arbitrary: M)
  case Nil then show ?case by auto
next
  case (Cons i xs)
  show ?case
  proof (cases "M 0 i + M i 0 ≤ 0 ∨ i = 0")
    case True
    note T = this
    show ?thesis
    proof (cases "i = 0")
      case False
      from Cons.prems have "0 ≤ n" "set [i] ⊆ {0..n}" by auto
      with Cons.prems(3) False T have "M 0 i + M i 0 = 0" by fastforce
      with Cons.IH[OF _ _ Cons.prems(3,4)] Cons.prems(1,2) show ?thesis by auto
    next
      case True
      with Cons.IH[OF _ _ Cons.prems(3,4)] Cons.prems(1,2) show ?thesis by auto
    qed
  next
    case False
    with Cons.prems have "0 < M 0 i + M i 0" "i ≤ n" "i ≠ 0" by auto
    with fix_index[OF this(1) cycle_free_diag_intro[OF Cons.prems(3)] Cons.prems(4) this(2,3), of v]
    obtain M' :: "('a DBMEntry) mat" where M':
      "((∃u. DBM_val_bounded v u M' n) ⟶ (∃u. DBM_val_bounded v u M n))" "(M' 0 i + M' i 0 = 0)"
      "cyc_free M' n" "∀j≤n. i ≠ j ∧ M 0 j + M j 0 > 0 ⟶ M' 0 j + M' j 0 > 0"
      "∀j. i ≠ j ∧ M 0 j + M j 0 = 0 ⟶ M' 0 j + M' j 0 = 0"
    using cycle_free_diag_equiv by blast
    let ?M' = "FW M' n"
    from fw_canonical[of n M'] ‹cyc_free M' n› have "canonical ?M' n" by auto
    from FW_cyc_free_preservation[OF ‹cyc_free M' n›] have "cyc_free ?M' n"
    by auto
    from FW_fixed_preservation[OF ‹i ≤ n› M'(2) ‹canonical ?M' n› ‹cyc_free ?M' n›]
    have fixed:"?M' 0 i + ?M' i 0 = 0" by (auto simp: add_mono)
    from Cons.IH[OF _ _ ‹cyc_free ?M' n› ‹canonical ?M' n›] Cons.prems(1,2,3)
    obtain M'' :: "('a DBMEntry) mat"
    where M'': "((∃u. DBM_val_bounded v u M'' n) ⟶ (∃u. DBM_val_bounded v u ?M' n))"
      "(∀i∈set xs. i ≠ 0 ⟶ M'' 0 i + M'' i 0 = 0)" "cyc_free M'' n"
      "(∀i≤n. i ∉ set xs ∧ ?M' 0 i + ?M' i 0 = 0 ⟶ M'' 0 i + M'' i 0 = 0)"
    by auto
    from FW_fixed_preservation[OF _ _ ‹canonical ?M' n› ‹cyc_free ?M' n›] M'(5)
    have "∀j≤n. i ≠ j ∧ M 0 j + M j 0 = 0 ⟶ ?M' 0 j + ?M' j 0 = 0" by auto
    with M''(4) have "∀j≤n. j ∉ set (i # xs) ∧ M 0 j + M j 0 = 0 ⟶ M'' 0 j + M'' j 0 = 0" by auto
    moreover from M''(2) M''(4) fixed Cons.prems(2) ‹i ≤ n›
    have "(∀i∈set (i#xs). i ≠ 0 ⟶ M'' 0 i + M'' i 0 = 0)" by auto
    moreover from M''(1) M'(1) FW_not_empty[of v _ M' n]
    have "(∃u. DBM_val_bounded v u M'' n) ⟶ (∃u. DBM_val_bounded v u M n)" by auto
    ultimately show ?thesis using ‹cyc_free M'' n› M''(4) by auto
  qed
qed

lemma cyc_free_obtains_valuation:
  "cyc_free M n ⟹ ∀ c. v c ≤ n ⟶ v c > 0 ⟹ ∃ u. DBM_val_bounded v u M n"
proof -
  assume A: "cyc_free M n" "∀ c. v c ≤ n ⟶ v c > 0"
  let ?M = "FW M n"
  from fw_canonical[of n M] A have "canonical ?M n" by auto
  from FW_cyc_free_preservation[OF A(1) ] have "cyc_free ?M n" .
  have "set [0..<n+1] ⊆ {0..n}" "distinct [0..<n+1]" by auto
  from fix_indices[OF this ‹cyc_free ?M n› ‹canonical ?M n›]
  obtain M' :: "('a DBMEntry) mat" where M':
    "(∃u. DBM_val_bounded v u M' n) ⟶ (∃u. DBM_val_bounded v u (FW M n) n)"
    "∀i∈set [0..<n + 1]. i ≠ 0 ⟶ M' 0 i + M' i 0 = 0" "cyc_free M' n"
    by blast
  let ?M' = "FW M' n"
  have "⋀ i. i ≤ n ⟹ i ∈ set [0..<n + 1]" by auto
  with M'(2) have M'_fixed: "∀i≤n. i ≠ 0 ⟶ M' 0 i + M' i 0 = 0" by fastforce
  from fw_canonical[of n M'] M'(3) have "canonical ?M' n" by blast
  from FW_fixed_preservation[OF _ _ this FW_cyc_free_preservation[OF M'(3)]] M'_fixed
  have fixed: "∀i≤n. i ≠ 0 ⟶ ?M' 0 i + ?M' i 0 = 0" by auto
  have *: "⋀i. i ≤ n ⟹ i ≠ 0 ⟹ ∃ d. ?M' 0 i = Le (-d) ∧ ?M' i 0 = Le d"
  proof -
    fix i assume i: "i ≤ n" "i ≠ 0"
    from i fixed have *:"dbm_add (?M' 0 i) (?M' i 0) = Le 0" by (auto simp add: add neutral)
    moreover
    { fix a b :: 'a assume "a + b = 0"
      then have "a = -b" by (simp add: eq_neg_iff_add_eq_0)
    }
    ultimately show "∃d. ?M' 0 i = Le (-d) ∧ ?M' i 0 = Le d"
    by (cases "?M' 0 i"; cases "?M' i 0"; simp)
  qed
  then obtain f where f: "∀ i≤n. i ≠ 0 ⟶ Le (f i) = ?M' i 0 ∧ Le (- f i) = ?M' 0 i" by metis
  let ?u = "λ c. f (v c)"
  have "DBM_val_bounded v ?u ?M' n"
    unfolding DBM_val_bounded_def
  proof (safe, goal_cases)
    case 1
    from cyc_free_diag_dest'[OF FW_cyc_free_preservation[OF M'(3)]] show ?case
    unfolding neutral less_eq by fast
  next
    case (2 c)
    with A(2) have **: "v c > 0" by auto
    with *[OF 2] obtain d where d: "Le (-d) = ?M' 0 (v c)" by auto
    with f 2 ** have "Le (- f (v c)) = Le (- d)" by simp
    then have "- f (v c) ≤ - d" by auto
    from dbm_entry_val.intros(2)[of ?u , OF this] d
    show ?case by auto
  next
    case (3 c)
    with A(2) have **: "v c > 0" by auto
    with *[OF 3] obtain d where d: "Le d = ?M' (v c) 0" by auto
    with f 3 ** have "Le (f (v c)) = Le d" by simp
    then have "f (v c) ≤ d" by auto
    from dbm_entry_val.intros(1)[of ?u, OF this] d
    show ?case by auto
  next
    case (4 c1 c2)
    with A(2) have **: "v c1 > 0" "v c2 > 0" by auto
    with *[OF 4(1)] obtain d1 where d1: "Le d1 = ?M' (v c1) 0" by auto
    with f 4 ** have "Le (f (v c1)) = Le d1" by simp
    then have d1': "f (v c1) = d1" by auto
    from *[OF 4(2)] ** obtain d2 where d2: "Le d2 = ?M' (v c2) 0" by auto
    with f 4 ** have "Le (f (v c2)) = Le d2" by simp
    then have d2': "f (v c2) = d2" by auto
    have "Le d1 ≤ ?M' (v c1) (v c2) + Le d2" using ‹canonical ?M' n› 4 d1 d2
      by (auto simp add: less_eq add)
    then show ?case
    proof (cases "?M' (v c1) (v c2)", goal_cases)
      case (1 d)
      then have "d1 ≤ d + d2" by (auto simp: add less_eq le_dbm_le)
      then have "d1 - d2 ≤ d" by (simp add: diff_le_eq)
      with 1 show ?case using d1' d2' by auto
    next
      case (2 d)
      then have "d1 < d + d2" by (auto simp: add less_eq dbm_le_def elim: dbm_lt.cases)
      then have "d1 - d2 < d" using diff_less_eq by blast
      with 2 show ?case using d1' d2' by auto
    qed auto
  qed
  from M'(1) FW_not_empty[OF this] obtain u where "DBM_val_bounded v u ?M n" by auto
  from FW_not_empty[OF this] show ?thesis by auto
qed

subsection ‹Floyd-Warshall and Empty DBMs›

theorem FW_detects_empty_zone:
  "∀k≤n. 0 < k ⟶ (∃c. v c = k) ⟹ ∀ c. v c ≤ n ⟶ v c > 0
  ⟹ [FW M n]⇘v,n⇙ = {} ⟷ (∃ i≤n. (FW M n) i i < Le 0)"
proof
  assume surj_on:"∀k≤n. 0 < k ⟶ (∃c. v c = k)" and "∃i≤n. (FW M n) i i < Le 0"
  then obtain i where *: "len (FW M n) i i [] < 0" "i ≤n" by (auto simp add: neutral)
  show "[FW M n]⇘v,n⇙ = {}"
  proof (rule ccontr, goal_cases)
    case 1
    then obtain u where "DBM_val_bounded v u (FW M n) n" unfolding DBM_zone_repr_def by auto
    from DBM_val_bounded_neg_cycle[OF this *(2) _ *(1) surj_on] show ?case by auto
  qed
next
  assume surj_on: "∀k≤n. 0 < k ⟶ (∃c. v c = k)" and empty: "[FW M n]⇘v,n⇙ = {}"
  and    cn: "∀ c. v c ≤ n ⟶ v c > 0"
  show "∃ i≤n. (FW M n) i i < Le 0"
  proof (rule ccontr, goal_cases)
    case 1
    then have *:"∀i≤n. FW M n i i ≥ 0" by (auto simp add: neutral)
    have "cyc_free M n"
    proof (rule ccontr)
      assume "¬ cyc_free M n"
      from FW_neg_cycle_detect[OF this] * show False by auto
    qed
    from FW_cyc_free_preservation[OF this] have "cyc_free (FW M n) n" .
    from cyc_free_obtains_valuation[OF ‹cyc_free (FW M n) n› cn] empty
    obtain u where "DBM_val_bounded v u (FW M n) n" by blast
    with empty show ?case by (auto simp add: DBM_zone_repr_def)
  qed
qed

(* This definition is "internal" to the theorems for the correctness of the Floyd-Warshall algorithm
   and we want to reuse this as a variable name, so we hide it away *)
hide_const (open) D

subsection ‹Mixed Corollaries›

lemma cyc_free_not_empty:
  assumes "cyc_free M n" "∀c. v c ≤ n ⟶ 0 < v c"
  shows "[(M :: ('a :: time) DBM)]⇘v,n⇙ ≠ {}"
using cyc_free_obtains_valuation[OF assms(1,2)] unfolding DBM_zone_repr_def by auto

lemma empty_not_cyc_free:
  assumes "∀c. v c ≤ n ⟶ 0 < v c" "[(M :: ('a :: time) DBM)]⇘v,n⇙ = {}"
  shows "¬ cyc_free M n"
using assms by (meson cyc_free_not_empty)

lemma not_empty_cyc_free:
  assumes "∀k≤n. 0 < k ⟶ (∃ c. v c = k)" "[(M :: ('a :: time) DBM)]⇘v,n⇙ ≠ {}"
  shows "cyc_free M n" using DBM_val_bounded_neg_cycle[OF _ _ _ _ assms(1)] assms(2)
unfolding DBM_zone_repr_def by fastforce

lemma neg_cycle_empty:
  assumes "∀k≤n. 0 < k ⟶ (∃ c. v c = k)" "set xs ⊆ {0..n}" "i ≤ n" "len M i i xs < 0"
  shows "[(M :: ('a :: time) DBM)]⇘v,n⇙ = {}" using assms
by (metis leD not_empty_cyc_free)

abbreviation clock_numbering' :: "('c ⇒ nat) ⇒ nat ⇒ bool"
where
  "clock_numbering' v n ≡ ∀ c. v c > 0 ∧ (∀x. ∀y. v x ≤ n ∧ v y ≤ n ∧ v x = v y ⟶ x = y)"

lemma non_empty_dbm_diag_set:
  "clock_numbering' v n ⟹ [M]⇘v,n⇙ ≠ {}
  ⟹ [M]⇘v,n⇙ = [(λ i j. if i = j then 0 else M i j)]⇘v,n⇙"
  unfolding DBM_zone_repr_def
proof (safe, goal_cases)
  case 1
  { fix c assume A: "v c = 0"
    from 1 have "v c > 0" by auto
    with A have False by auto
  } note * = this
  from 1 have [simp]: "Le 0 ≼ M 0 0" by (auto simp: DBM_val_bounded_def)
  note [simp] = neutral
  from 1 show ?case
    unfolding DBM_val_bounded_def
    apply safe
    subgoal
      using * by simp
    subgoal
      using * by (metis (full_types))
    subgoal
      using * by (metis (full_types))
    subgoal for c1 c2
      by (cases "c1 = c2") auto
    done
next
  case (2 x xa)
  note G = this
  { fix c assume A: "v c = 0"
    from 2 have "v c > 0" by auto
    with A have False by auto
  } note * = this
  { fix c assume A: "v c ≤ n" "M (v c) (v c) < 0"
    with 2 have False
      by (fastforce simp: neutral DBM_val_bounded_def less elim!: dbm_lt.cases)
  } note ** = this
  from 2 have [simp]: "Le 0 ≼ M 0 0" by (auto simp: DBM_val_bounded_def)
  note [simp] = neutral
  from 2 show ?case
    unfolding DBM_val_bounded_def
  proof (safe, goal_cases)
    case 1 with * show ?case by simp presburger
    case 2 with * show ?case by presburger
  next
    case (3 c1 c2)
    show ?case
    proof (cases "v c1 = v c2")
      case True
      with 3 have "c1 = c2" by auto
      moreover from this **[OF 3(9)] not_less have "M (v c2) (v c2) ≥ 0" by auto
      ultimately show "dbm_entry_val xa (Some c1) (Some c2) (M (v c1) (v c2))" unfolding neutral
      by (cases "M (v c1) (v c2)") (auto simp add: less_eq dbm_le_def, fastforce+)
    next
      case False
      with 3 show ?thesis by presburger
    qed
  qed
qed

lemma non_empty_cycle_free:
  assumes "[M]⇘v,n⇙ ≠ {}"
    and "∀k≤n. 0 < k ⟶ (∃c. v c = k)"
  shows "cycle_free M n"
apply (rule ccontr)
apply (drule negative_cycle_dest_diag')
using DBM_val_bounded_neg_cycle assms unfolding DBM_zone_repr_def by blast

lemma neg_diag_empty:
  assumes "∀k≤n. 0 < k ⟶ (∃c. v c = k)" "i ≤ n" "M i i < 0"
  shows "[M]⇘v,n⇙ = {}"
unfolding DBM_zone_repr_def using DBM_val_bounded_neg_cycle[of v _ M n i "[]"] assms by auto

lemma canonical_empty_zone:
  assumes "∀k≤n. 0 < k ⟶ (∃c. v c = k)" "∀c. v c ≤ n ⟶ 0 < v c"
    and "canonical M n"
  shows "[M]⇘v,n⇙ = {} ⟷ (∃i≤n. M i i < 0)"
using FW_detects_empty_zone[OF assms(1,2), of M] FW_canonical_id[OF assms(3)] unfolding neutral
by simp

section ‹Orderings of DBMs›

lemma canonical_saturated_1:
  assumes "Le r ≤ M (v c1) 0"
    and "Le (- r) ≤ M 0 (v c1)"
    and "cycle_free M n"
    and "canonical M n"
    and "v c1 ≤ n"
    and "v c1 > 0"
    and "∀c. v c ≤ n ⟶ 0 < v c"
  obtains u where "u ∈ [M]⇘v,n⇙" "u c1 = r"
proof -
  let ?M' = "λi' j'. if i'=v c1 ∧ j'=0 then Le r else if i'=0 ∧ j'=v c1 then Le (- r) else M i' j'"
  from fix_index'[OF assms(1-5)] assms(6) have M':
    "∀u. DBM_val_bounded v u ?M' n ⟶ DBM_val_bounded v u M n"
    "cycle_free ?M' n" "?M' (v c1) 0 = Le r" "?M' 0 (v c1) = Le (- r)"
  by auto
  with cyc_free_obtains_valuation[unfolded cycle_free_diag_equiv, of ?M' n v] assms(7) obtain u where
    u: "DBM_val_bounded v u ?M' n"
  by fastforce
  with assms(5,6) M'(3,4) have "u c1 = r" unfolding DBM_val_bounded_def by fastforce
  moreover from u M'(1) have "u ∈ [M]⇘v,n⇙" unfolding DBM_zone_repr_def by auto
  ultimately show thesis by (auto intro: that)
qed

lemma canonical_saturated_2:
  assumes "Le r ≤ M 0 (v c2)"
    and "Le (- r) ≤ M (v c2) 0"
    and "cycle_free M n"
    and "canonical M n"
    and "v c2 ≤ n"
    and "v c2 > 0"
    and "∀c. v c ≤ n ⟶ 0 < v c"
  obtains u where "u ∈ [M]⇘v,n⇙" "u c2 = - r"
proof -
  let ?M' = "λi' j'. if i'=0 ∧ j'=v c2 then Le r else if i'=v c2 ∧ j'=0 then Le (-r) else M i' j'"
  from fix_index'[OF assms(1-4)] assms(5,6) have M':
    "∀u. DBM_val_bounded v u ?M' n ⟶ DBM_val_bounded v u M n"
    "cycle_free ?M' n" "?M' 0 (v c2) = Le r" "?M' (v c2) 0 = Le (- r)"
  by auto
  with cyc_free_obtains_valuation[unfolded cycle_free_diag_equiv, of ?M' n v] assms(7) obtain u where
    u: "DBM_val_bounded v u ?M' n"
  by fastforce
  with assms(5,6) M'(3,4) have "u c2 ≤ -r" "- u c2 ≤ r" unfolding DBM_val_bounded_def by fastforce+
  then have "u c2 = -r" by (simp add: le_minus_iff)
  moreover from u M'(1) have "u ∈ [M]⇘v,n⇙" unfolding DBM_zone_repr_def by auto
  ultimately show thesis by (auto intro: that)
qed

lemma canonical_saturated_3:
  assumes "Le r ≤ M (v c1) (v c2)"
    and "Le (- r) ≤ M (v c2) (v c1)"
    and "cycle_free M n"
    and "canonical M n"
    and "v c1 ≤ n" "v c2 ≤ n"
    and "v c1 ≠ v c2"
    and "∀c. v c ≤ n ⟶ 0 < v c"
  obtains u where "u ∈ [M]⇘v,n⇙" "u c1 - u c2 = r"
proof -
  let ?M'="λi' j'. if i'=v c1 ∧ j'=v c2 then Le r else if i'=v c2 ∧ j'=v c1 then Le (-r) else M i' j'"
  from fix_index'[OF assms(1-7), of v] assms(7,8) have M':
    "∀u. DBM_val_bounded v u ?M' n ⟶ DBM_val_bounded v u M n"
    "cycle_free ?M' n" "?M' (v c1) (v c2) = Le r" "?M' (v c2) (v c1) = Le (- r)"
  by auto
  with cyc_free_obtains_valuation[unfolded cycle_free_diag_equiv, of ?M' n v] assms obtain u where u:
    "DBM_val_bounded v u ?M' n"
  by fastforce
  with assms(5,6) M'(3,4) have
    "u c1 - u c2 ≤ r" "u c2 - u c1 ≤ - r"
  unfolding DBM_val_bounded_def by fastforce+
  then have "u c1 - u c2 = r" by (simp add: le_minus_iff)
  moreover from u M'(1) have "u ∈ [M]⇘v,n⇙" unfolding DBM_zone_repr_def by auto
  ultimately show thesis by (auto intro: that)
qed

lemma DBM_canonical_subset_le:
  notes any_le_inf[intro]
  fixes M :: "real DBM"
  assumes "canonical M n" "[M]⇘v,n⇙ ⊆ [M']⇘v,n⇙" "[M]⇘v,n⇙ ≠ {}" "i ≤ n" "j ≤ n" "i ≠ j"
  assumes clock_numbering: "clock_numbering' v n"
                           "∀k≤n. 0 < k ⟶ (∃c. v c = k)"
  shows "M i j ≤ M' i j"
proof -
  from non_empty_cycle_free[OF assms(3)] clock_numbering(2) have "cycle_free M n" by auto
  with assms(1,4,5) have non_neg:
    "M i j + M j i ≥ Le 0"
  by (metis cycle_free_diag order.trans neutral)

  from clock_numbering have cn: "∀c. v c ≤ n ⟶ 0 < v c" by auto
  show ?thesis
  proof (cases "i = 0")
    case True
    show ?thesis
    proof (cases "j = 0")
      case True
      with assms ‹i = 0› show ?thesis
      unfolding neutral DBM_zone_repr_def DBM_val_bounded_def less_eq by auto
    next
      case False
      then have "j > 0" by auto
      with ‹j ≤ n› clock_numbering obtain c2 where c2: "v c2 = j" by auto
      note t = canonical_saturated_2[OF _ _ ‹cycle_free M n› assms(1) assms(5)[folded c2] _ cn,unfolded c2]
      show ?thesis
      proof (rule ccontr, goal_cases)
        case 1
        { fix d assume 1: "M 0 j = ∞"
          obtain r where r: "Le r ≤ M 0 j" "Le (-r) ≤ M j 0" "d < r"
          proof (cases "M j 0")
            case (Le d')
            obtain r where "r > - d'" using gt_ex by blast
            with Le 1 show ?thesis by (intro that[of "max r (d + 1)"]) auto
          next
            case (Lt d')
            obtain r where "r > - d'" using gt_ex by blast
            with Lt 1 show ?thesis by (intro that[of "max r (d + 1)"]) auto
          next
            case INF
            with 1 show ?thesis by (intro that[of "d + 1"]) auto
          qed
          then have "∃ r. Le r ≤ M 0 j ∧ Le (-r) ≤ M j 0 ∧ d < r" by auto
        } note inf_case = this
        { fix a b d :: real assume 1: "a < b" assume b: "b + d > 0"
          then have *: "b > -d" by auto
          obtain r where "r > - d" "r > a" "r < b"
          proof (cases "a ≥ - d")
            case True
            from 1 obtain r where "r > a" "r < b" using dense by auto
            with True show ?thesis by (auto intro: that[of r])
          next
            case False
            with * obtain r where "r > -d" "r < b" using dense by auto
            with False show ?thesis by (auto intro: that[of r])
          qed
          then have "∃ r. r > -d ∧ r > a ∧ r < b" by auto
        } note gt_case = this
        { fix a r assume r: "Le r ≤ M 0 j" "Le (-r) ≤ M j 0" "a < r" "M' 0 j = Le a ∨ M' 0 j = Lt a"
          from t[OF this(1,2) ‹0 < j›] obtain u where u: "u ∈ [M]⇘v,n⇙" "u c2 = - r" .
          with ‹j ≤ n› c2 assms(2) have "dbm_entry_val u None (Some c2) (M' 0 j)"
          unfolding DBM_zone_repr_def DBM_val_bounded_def by blast
          with u(2) r(3,4) have False by auto
        } note contr = this
        from 1 True have "M' 0 j < M 0 j" by auto
        then show False unfolding less
        proof (cases rule: dbm_lt.cases)
          case (1 d)
          with inf_case obtain r where r: "Le r ≤ M 0 j" "Le (-r) ≤ M j 0" "d < r" by auto
          from contr[OF this] 1 show False by fast
        next
          case (2 d)
          with inf_case obtain r where r: "Le r ≤ M 0 j" "Le (-r) ≤ M j 0" "d < r" by auto
          from contr[OF this] 2 show False by fast
        next
          case (3 a b)
          obtain r where r: "Le r ≤ M 0 j" "Le (-r) ≤ M j 0" "a < r"
          proof (cases "M j 0")
            case (Le d')
            with 3 non_neg ‹i = 0› have "b + d' ≥ 0" unfolding add by auto
            then have "b ≥ - d'" by auto
            with 3 obtain r where "r ≥ - d'" "r > a" "r ≤ b" by blast
            with Le 3 show ?thesis by (intro that[of r]) auto
          next
            case (Lt d')
            with 3 non_neg ‹i = 0› have "b + d' > 0" unfolding add by auto
            from gt_case[OF 3(3) this] obtain r where "r > - d'" "r > a" "r ≤ b" by auto
            with Lt 3 show ?thesis by (intro that[of r]) auto
          next
            case INF
            with 3 show ?thesis by (intro that[of b]) auto
          qed
          from contr[OF this] 3 show False by fast
        next
          case (4 a b)
          obtain r where r: "Le r ≤ M 0 j" "Le (-r) ≤ M j 0" "a < r"
          proof (cases "M j 0")
            case (Le d)
            with 4 non_neg ‹i = 0› have "b + d > 0" unfolding add by auto
            from gt_case[OF 4(3) this] obtain r where "r > - d" "r > a" "r < b" by auto
            with Le 4 show ?thesis by (intro that[of r]) auto
          next
            case (Lt d)
            with 4 non_neg ‹i = 0› have "b + d > 0" unfolding add by auto
            from gt_case[OF 4(3) this] obtain r where "r > - d" "r > a" "r < b" by auto
            with Lt 4 show ?thesis by (intro that[of r]) auto
          next
            case INF
            from 4 dense obtain r where "r > a" "r < b" by auto
            with 4 INF show ?thesis by (intro that[of r]) auto
          qed
          from contr[OF this] 4 show False by fast
        next
          case (5 a b)
          obtain r where r: "Le r ≤ M 0 j" "Le (-r) ≤ M j 0" "a ≤ r"
          proof (cases "M j 0")
            case (Le d')
            with 5 non_neg ‹i = 0› have "b + d' ≥ 0" unfolding add by auto
            then have "b ≥ - d'" by auto
            with 5 obtain r where "r ≥ - d'" "r ≥ a" "r ≤ b" by blast
            with Le 5 show ?thesis by (intro that[of r]) auto
          next
            case (Lt d')
            with 5 non_neg ‹i = 0› have "b + d' > 0" unfolding add by auto
            then have "b > - d'" by auto
            with 5 obtain r where "r > - d'" "r ≥ a" "r ≤ b" by blast
            with Lt 5 show ?thesis by (intro that[of r]) auto
          next
            case INF
            with 5 show ?thesis by (intro that[of b]) auto
          qed
          from t[OF this(1,2) ‹j > 0›] obtain u where u: "u ∈ [M]⇘v,n⇙" "u c2 = - r" .
          with ‹j ≤ n› c2 assms(2) have "dbm_entry_val u None (Some c2) (M' 0 j)"
          unfolding DBM_zone_repr_def DBM_val_bounded_def by blast
          with u(2) r(3) 5 show False by auto
        next
          case (6 a b)
          obtain r where r: "Le r ≤ M 0 j" "Le (-r) ≤ M j 0" "a < r"
          proof (cases "M j 0")
            case (Le d)
            with 6 non_neg ‹i = 0› have "b + d > 0" unfolding add by auto
            from gt_case[OF 6(3) this] obtain r where "r > - d" "r > a" "r < b" by auto
            with Le 6 show ?thesis by (intro that[of r]) auto
          next
            case (Lt d)
            with 6 non_neg ‹i = 0› have "b + d > 0" unfolding add by auto
            from gt_case[OF 6(3) this] obtain r where "r > - d" "r > a" "r < b" by auto
            with Lt 6 show ?thesis by (intro that[of r]) auto
          next
            case INF
            from 6 dense obtain r where "r > a" "r < b" by auto
            with 6 INF show ?thesis by (intro that[of r]) auto
          qed
          from contr[OF this] 6 show False by fast
        qed
      qed
    qed
  next
    case False
    then have "i > 0" by auto
    with ‹i ≤ n› clock_numbering obtain c1 where c1: "v c1 = i" by auto
    show ?thesis
    proof (cases "j = 0")
      case True
      note t = canonical_saturated_1[OF _ _ ‹cycle_free M n› assms(1) assms(4)[folded c1] _ cn,
                                     unfolded c1]
      show ?thesis
      proof (rule ccontr, goal_cases)
        case 1
        { fix d assume 1: "M i 0 = ∞"
          obtain r where r: "Le r ≤ M i 0" "Le (-r) ≤ M 0 i" "d < r"
          proof (cases "M 0 i")
            case (Le d')
            obtain r where "r > - d'" using gt_ex by blast
            with Le 1 show ?thesis by (intro that[of "max r (d + 1)"]) auto
          next
            case (Lt d')
            obtain r where "r > - d'" using gt_ex by blast
            with Lt 1 show ?thesis by (intro that[of "max r (d + 1)"]) auto
          next
            case INF
            with 1 show ?thesis by (intro that[of "d + 1"]) auto
          qed
          then have "∃ r. Le r ≤ M i 0 ∧ Le (-r) ≤ M 0 i ∧ d < r" by auto
        } note inf_case = this
        { fix a b d :: real assume 1: "a < b" assume b: "b + d > 0"
          then have *: "b > -d" by auto
          obtain r where "r > - d" "r > a" "r < b"
          proof (cases "a ≥ - d")
            case True
            from 1 obtain r where "r > a" "r < b" using dense by auto
            with True show ?thesis by (auto intro: that[of r])
          next
            case False
            with * obtain r where "r > -d" "r < b" using dense by auto
            with False show ?thesis by (auto intro: that[of r])
          qed
          then have "∃ r. r > -d ∧ r > a ∧ r < b" by auto
        } note gt_case = this
        { fix a r assume r: "Le r ≤ M i 0" "Le (-r) ≤ M 0 i" "a < r" "M' i 0 = Le a ∨ M' i 0 = Lt a"
          from t[OF this(1,2) ‹i > 0›] obtain u where u: "u ∈ [M]⇘v,n⇙" "u c1 = r" .
          with ‹i ≤ n› c1 assms(2) have "dbm_entry_val u (Some c1) None (M' i 0)"
          unfolding DBM_zone_repr_def DBM_val_bounded_def by blast
          with u(2) r(3,4) have False by auto
        } note contr = this
        from 1 True have "M' i 0 < M i 0" by auto
        then show False unfolding less
        proof (cases rule: dbm_lt.cases)
          case (1 d)
          with inf_case obtain r where r: "Le r ≤ M i 0" "Le (-r) ≤ M 0 i" "d < r" by auto
          from contr[OF this] 1 show False by fast
        next
          case (2 d)
          with inf_case obtain r where r: "Le r ≤ M i 0" "Le (-r) ≤ M 0 i" "d < r" by auto
          from contr[OF this] 2 show False by fast
        next
          case (3 a b)
          obtain r where r: "Le r ≤ M i 0" "Le (-r) ≤ M 0 i" "a < r"
          proof (cases "M 0 i")
            case (Le d')
            with 3 non_neg ‹j = 0› have "b + d' ≥ 0" unfolding add by auto
            then have "b ≥ - d'" by auto
            with 3 obtain r where "r ≥ - d'" "r > a" "r ≤ b" by blast
            with Le 3 show ?thesis by (intro that[of r]) auto
          next
            case (Lt d')
            with 3 non_neg ‹j = 0› have "b + d' > 0" unfolding add by auto
            from gt_case[OF 3(3) this] obtain r where "r > - d'" "r > a" "r ≤ b" by auto
            with Lt 3 show ?thesis by (intro that[of r]) auto
          next
            case INF
            with 3 show ?thesis by (intro that[of b]) auto
          qed
          from contr[OF this] 3 show False by fast
        next
          case (4 a b)
          obtain r where r: "Le r ≤ M i 0" "Le (-r) ≤ M 0 i" "a < r"
          proof (cases "M 0 i")
            case (Le d)
            with 4 non_neg ‹j = 0› have "b + d > 0" unfolding add by auto
            from gt_case[OF 4(3) this] obtain r where "r > - d" "r > a" "r < b" by auto
            with Le 4 show ?thesis by (intro that[of r]) auto
          next
            case (Lt d)
            with 4 non_neg ‹j = 0› have "b + d > 0" unfolding add by auto
            from gt_case[OF 4(3) this] obtain r where "r > - d" "r > a" "r < b" by auto
            with Lt 4 show ?thesis by (intro that[of r]) auto
          next
            case INF
            from 4 dense obtain r where "r > a" "r < b" by auto
            with 4 INF show ?thesis by (intro that[of r]) auto
          qed
          from contr[OF this] 4 show False by fast
        next
          case (5 a b)
          obtain r where r: "Le r ≤ M i 0" "Le (-r) ≤ M 0 i" "a ≤ r"
          proof (cases "M 0 i")
            case (Le d')
            with 5 non_neg ‹j = 0› have "b + d' ≥ 0" unfolding add by auto
            then have "b ≥ - d'" by auto
            with 5 obtain r where "r ≥ - d'" "r ≥ a" "r ≤ b" by blast
            with Le 5 show ?thesis by (intro that[of r]) auto
          next
            case (Lt d')
            with 5 non_neg ‹j = 0› have "b + d' > 0" unfolding add by auto
            then have "b > - d'" by auto
            with 5 obtain r where "r > - d'" "r ≥ a" "r ≤ b" by blast
            with Lt 5 show ?thesis by (intro that[of r]) auto
          next
            case INF
            with 5 show ?thesis by (intro that[of b]) auto
          qed
          from t[OF this(1,2) ‹i > 0›] obtain u where u: "u ∈ [M]⇘v,n⇙" "u c1 = r" .
          with ‹i ≤ n› c1 assms(2) have "dbm_entry_val u (Some c1) None (M' i 0)"
          unfolding DBM_zone_repr_def DBM_val_bounded_def by blast
          with u(2) r(3) 5 show False by auto
        next
          case (6 a b)
          obtain r where r: "Le r ≤ M i 0" "Le (-r) ≤ M 0 i" "a < r"
          proof (cases "M 0 i")
            case (Le d)
            with 6 non_neg ‹j = 0› have "b + d > 0" unfolding add by auto
            from gt_case[OF 6(3) this] obtain r where "r > - d" "r > a" "r < b" by auto
            with Le 6 show ?thesis by (intro that[of r]) auto
          next
            case (Lt d)
            with 6 non_neg ‹j = 0› have "b + d > 0" unfolding add by auto
            from gt_case[OF 6(3) this] obtain r where "r > - d" "r > a" "r < b" by auto
            with Lt 6 show ?thesis by (intro that[of r]) auto
          next
            case INF
            from 6 dense obtain r where "r > a" "r < b" by auto
            with 6 INF show ?thesis by (intro that[of r]) auto
          qed
          from contr[OF this] 6 show False by fast
        qed
      qed
    next
      case False
      then have "j > 0" by auto
      with ‹j ≤ n› clock_numbering obtain c2 where c2: "v c2 = j" by auto
      note t = canonical_saturated_3[OF _ _ ‹cycle_free M n› assms(1) assms(4)[folded c1]
                                        assms(5)[folded c2] _ cn, unfolded c1 c2]
      show ?thesis
      proof (rule ccontr, goal_cases)
        case 1
        { fix d assume 1: "M i j = ∞"
          obtain r where r: "Le r ≤ M i j" "Le (-r) ≤ M j i" "d < r"
          proof (cases "M j i")
            case (Le d')
            obtain r where "r > - d'" using gt_ex by blast
            with Le 1 show ?thesis by (intro that[of "max r (d + 1)"]) auto
          next
            case (Lt d')
            obtain r where "r > - d'" using gt_ex by blast
            with Lt 1 show ?thesis by (intro that[of "max r (d + 1)"]) auto
          next
            case INF
            with 1 show ?thesis by (intro that[of "d + 1"]) auto
          qed
          then have "∃ r. Le r ≤ M i j ∧ Le (-r) ≤ M j i ∧ d < r" by auto
        } note inf_case = this
        { fix a b d :: real assume 1: "a < b" assume b: "b + d > 0"
          then have *: "b > -d" by auto
          obtain r where "r > - d" "r > a" "r < b"
          proof (cases "a ≥ - d")
            case True
            from 1 obtain r where "r > a" "r < b" using dense by auto
            with True show ?thesis by (auto intro: that[of r])
          next
            case False
            with * obtain r where "r > -d" "r < b" using dense by auto
            with False show ?thesis by (auto intro: that[of r])
          qed
          then have "∃ r. r > -d ∧ r > a ∧ r < b" by auto
        } note gt_case = this
        { fix a r assume r: "Le r ≤ M i j" "Le (-r) ≤ M j i" "a < r" "M' i j = Le a ∨ M' i j = Lt a"
          from t[OF this(1,2) ‹i ≠ j›] obtain u where u: "u ∈ [M]⇘v,n⇙" "u c1 - u c2 = r" .
          with ‹i ≤ n› ‹j ≤ n› c1 c2 assms(2) have "dbm_entry_val u (Some c1) (Some c2) (M' i j)"
          unfolding DBM_zone_repr_def DBM_val_bounded_def by blast
          with u(2) r(3,4) have False by auto
        } note contr = this
        from 1 have "M' i j < M i j" by auto
        then show False unfolding less
        proof (cases rule: dbm_lt.cases)
          case (1 d)
          with inf_case obtain r where r: "Le r ≤ M i j" "Le (-r) ≤ M j i" "d < r" by auto
          from contr[OF this] 1 show False by fast
        next
          case (2 d)
          with inf_case obtain r where r: "Le r ≤ M i j" "Le (-r) ≤ M j i" "d < r" by auto
          from contr[OF this] 2 show False by fast
        next
          case (3 a b)
          obtain r where r: "Le r ≤ M i j" "Le (-r) ≤ M j i" "a < r"
          proof (cases "M j i")
            case (Le d')
            with 3 non_neg have "b + d' ≥ 0" unfolding add by auto
            then have "b ≥ - d'" by auto
            with 3 obtain r where "r ≥ - d'" "r > a" "r ≤ b" by blast
            with Le 3 show ?thesis by (intro that[of r]) auto
          next
            case (Lt d')
            with 3 non_neg have "b + d' > 0" unfolding add by auto
            from gt_case[OF 3(3) this] obtain r where "r > - d'" "r > a" "r ≤ b" by auto
            with Lt 3 show ?thesis by (intro that[of r]) auto
          next
            case INF
            with 3 show ?thesis by (intro that[of b]) auto
          qed
          from contr[OF this] 3 show False by fast
        next
          case (4 a b)
          obtain r where r: "Le r ≤ M i j" "Le (-r) ≤ M j i" "a < r"
          proof (cases "M j i")
            case (Le d)
            with 4 non_neg have "b + d > 0" unfolding add by auto
            from gt_case[OF 4(3) this] obtain r where "r > - d" "r > a" "r < b" by auto
            with Le 4 show ?thesis by (intro that[of r]) auto
          next
            case (Lt d)
            with 4 non_neg have "b + d > 0" unfolding add by auto
            from gt_case[OF 4(3) this] obtain r where "r > - d" "r > a" "r < b" by auto
            with Lt 4 show ?thesis by (intro that[of r]) auto
          next
            case INF
            from 4 dense obtain r where "r > a" "r < b" by auto
            with 4 INF show ?thesis by (intro that[of r]) auto
          qed
          from contr[OF this] 4 show False by fast
        next
          case (5 a b)
          obtain r where r: "Le r ≤ M i j" "Le (-r) ≤ M j i" "a ≤ r"
          proof (cases "M j i")
            case (Le d')
            with 5 non_neg have "b + d' ≥ 0" unfolding add by auto
            then have "b ≥ - d'" by auto
            with 5 obtain r where "r ≥ - d'" "r ≥ a" "r ≤ b" by blast
            with Le 5 show ?thesis by (intro that[of r]) auto
          next
            case (Lt d')
            with 5 non_neg have "b + d' > 0" unfolding add by auto
            then have "b > - d'" by auto
            with 5 obtain r where "r > - d'" "r ≥ a" "r ≤ b" by blast
            with Lt 5 show ?thesis by (intro that[of r]) auto
          next
            case INF
            with 5 show ?thesis by (intro that[of b]) auto
          qed
          from t[OF this(1,2) ‹i ≠ j›] obtain u where u: "u ∈ [M]⇘v,n⇙" "u c1 - u c2= r" .
          with ‹i ≤ n› ‹j ≤ n› c1 c2 assms(2) have "dbm_entry_val u (Some c1) (Some c2) (M' i j)"
          unfolding DBM_zone_repr_def DBM_val_bounded_def by blast
          with u(2) r(3) 5 show False by auto
        next
          case (6 a b)
          obtain r where r: "Le r ≤ M i j" "Le (-r) ≤ M j i" "a < r"
          proof (cases "M j i")
            case (Le d)
            with 6 non_neg have "b + d > 0" unfolding add by auto
            from gt_case[OF 6(3) this] obtain r where "r > - d" "r > a" "r < b" by auto
            with Le 6 show ?thesis by (intro that[of r]) auto
          next
            case (Lt d)
            with 6 non_neg have "b + d > 0" unfolding add by auto
            from gt_case[OF 6(3) this] obtain r where "r > - d" "r > a" "r < b" by auto
            with Lt 6 show ?thesis by (intro that[of r]) auto
          next
            case INF
            from 6 dense obtain r where "r > a" "r < b" by auto
            with 6 INF show ?thesis by (intro that[of r]) auto
          qed
          from contr[OF this] 6 show False by fast
        qed
      qed
    qed
  qed
qed

end