proposition: Lemma setIdP x pA pB : reflect (pA x /\ pB x) (x \in [set y | pA y & pB y]).
proof: Proof. by rewrite !inE; apply: andP. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop)