proposition: Lemma quotP P : (forall y : T, repr (\pi_qT y) = y -> P (\pi_qT y)) -> forall x : qT, P x.
proof: Proof. by move=> Py x; rewrite -[x]reprK; apply: Py; rewrite reprK. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice) mathcomp(seq fintype)