proposition: Fact ecpU_subproof : cancel3 ecp_edge ecpU_node ecpU_face.
proof: Proof. move=> [||x] //=; first by rewrite eqxx. by case: ifP => /= [/eqP <- | ->]; rewrite edgeK. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype path fingraph) fourcolor(hypermap geometry color)