IMP --- A WHILE-language and its Semantics
The denotational, operational, and axiomatic semantics, a verification
condition generator, and all the necessary soundness, completeness and
equivalence proofs. Essentially a formalization of the first 100 pages
of
@book{Winskel, author = {Glynn Winskel},
title = {The Formal Semantics of Programming Languages},
publisher = {MIT Press}, year = 1993}
An eminently readable description of this theory is found
here.