proposition: Fact comp_is_join_morphism : join_morphism (f \o g).
proof: Proof. by move=> x y; rewrite /= !omorphU. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(path fintype tuple bigop finset div prime finfun) mathcomp(finset)