proposition: Lemma sub_cface_injcp cp1 cp2 : {homo @injcp cp1 cp2 : x y / cface x y}.
proof: Proof. elim: cp1 cp2 => [|s cp1 IHcp] cp2 x y xFy //; case: s => *; apply: IHcp => //. - by rewrite cface_icpY. - by rewrite cface_icpH. - by rewrite cface_icpU. - by rewrite cface_icpK. exact: sub_cface_icpA. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype path fingraph) fourcolor(hypermap geometry color)