fact: Variable f_compat : forall a a', eqA a a' -> eqB (f a) (f a').
imports: Coq(RelationClasses Setoid Morphisms SetoidList Mergesort Permutation) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq fintype) mathcomp(bigop path) RegexpBrzozowski(glue)