proposition: Lemma setX2_canon_axiom x y: lf_axiom (fun z => variantLc (P z) (Q z)) (x \times y) (product2 x y).
proof: Proof. move=> t /setX_P [pt px qy]; apply/setX2_P;aw; split;fprops. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat)