proposition: Lemma oopA_subdef : associative oop.
proof: Proof. by move=> [x|] [y|] [z|]//; rewrite /oAC/= opA. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq path) mathcomp(div fintype tuple finfun)