proposition: Lemma size_cpring_ecpA : size (cpring ecpA) = sub2ifgt2 (size (cpring x0)).
proof: Proof. rewrite cpring_ecpA /=; have [x0gt2|] :=boolP (long_cpring x0). by rewrite head_long_cpring. by rewrite size_long_cpring; case: (size _) => [|[|[|n]]]. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype path fingraph) fourcolor(hypermap geometry color)