proposition: Lemma lift_eqn (ix iy : I) (x : G ix) (y : G iy) : ix != iy -> lift_edge (existT ix x) (existT iy y) = false.
proof: Proof. by rewrite /lift_edge /= => /negbTE ->. Qed.
imports: Relations Recdef mathcomp.ssreflect.ssreflect mathcomp(all_ssreflect) CompDecModal.libs(edone bcase fset base)