proposition: Lemma fproperUr A B : ~~ (A `<=` B) -> B `<` A `|` B.
proof: Proof. by rewrite fproperE fsubsetUr fsubUset fsubset_refl /= andbT. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrnat eqtype ssrfun seq) mathcomp(choice path finset finfun fintype bigop)