Abstract
We apply Andy Pitts's methods of defining relations over domains to
several classical results in the literature. We show that the Y
combinator coincides with the domain-theoretic fixpoint operator,
that parallel-or and the Plotkin existential are not definable in
PCF, that the continuation semantics for PCF coincides with the
direct semantics, and that our domain-theoretic semantics for PCF is
adequate for reasoning about contextual equivalence in an
operational semantics. Our version of PCF is untyped and has both
strict and non-strict function abstractions. The development is
carried out in HOLCF.