proposition: Fact cube_cancel3 : cancel3 cube_edge cube_node cube_face.
proof: Proof. by do 2![case]=> x; rewrite /= ?faceK ?edgeK ?nodeK. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype path fingraph) fourcolor(hypermap geometry color coloring)