proposition: Lemma fset_eqP {A B} : reflect (A =i B) (A == B).
proof: Proof. exact: (equivP eqP (iff_sym fsetP)). Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrnat eqtype ssrfun seq) mathcomp(choice path finset finfun fintype bigop)