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