We compare the styles of several proof assistants for mathematics. We present Pythagoras’ proof of the irrationality of √ 2 both informal and formalized in (1) HOL, (2) Mizar, (3) PVS, (4) Coq, (5)… (More)

This paper contains a proof–theoretic account of unification in intermediate logics. It is shown that many existing results can be extended to fragments that at least contain implication and… (More)

A well-known problem in intuitionistic logic is the existence of valid but not derivable rules. This problem seems to be related with some constructive features of intuitionism (disjunction and… (More)