BibTeX: 
@article{FOL_Seq_Calc1AFP,
author = {Andreas Halkjær From},
title = {A Sequent Calculus for FirstOrder Logic},
journal = {Archive of Formal Proofs},
month = jul,
year = 2019,
note = {\url{http://isaafp.org/entries/FOL_Seq_Calc1.html},
Formal proof development},
ISSN = {2150914x},
}
