proposition: Lemma tofracD : {morph tofrac: x y / x + y}.
proof: Proof. exact: rmorphD. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(ssrAC choice tuple bigop ssralg poly polydiv) mathcomp(generic_quotient)