proposition: Lemma mem_restrictf f (A : {fset K}) (k : K) : k \in f.[& A] = (k \in A) && (k \in f) :> bool.
proof: Proof. by rewrite mem_filterf andbC. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrnat eqtype ssrfun seq) mathcomp(choice path finset finfun fintype bigop)