fact: Definition set_pair_der (E F:bregexp) : gset (bregexp*bregexp) := fun G => let (e,f) := G in exists2 s, similar e (wder s E) & similar f (wder s F).
imports: Coq(RelationClasses) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq fintype) mathcomp(bigop path) RegLang(languages) RegexpBrzozowski(glue gfinset regexp finite_der)