proposition: Lemma size_cpring_ecpR : size (cpring (pointer ecpR)) = size (cpring x0).
proof: Proof. by rewrite cpring_ecpR size_rot. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype path fingraph) fourcolor(hypermap geometry color)