proposition: Lemma pi_inv : {morph \pi : x / invf x >-> inv x}.
proof: Proof. move=> x; unlock inv; apply/eqmodP=> /=; rewrite equivfE /invf eq_sym. do 2?case: RatioP=> /= [/eqP|]; rewrite ?mul0r ?mul1r -?equivf_def ?numer0 ?reprK //. by move=> hx /eqP hx'; rewrite hx' eqxx in hx. by move=> /eqP ->; rewrite eqxx. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(ssrAC choice tuple bigop ssralg poly polydiv) mathcomp(generic_quotient)