proposition: Lemma imset2_pair (A : {set aT}) (B : {set aT2}) : [set (x, y) | x in A, y in B] = setX A B.
proof: Proof. apply/setP=> [[x y]]; rewrite !inE /=. by apply/imset2P/andP=> [[_ _ _ _ [-> ->]//]| []]; exists x y. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop)