proposition: Lemma end0g_node d : end0g (gnode d) = end0g d.
proof: Proof. by rewrite /end0g halfg_node oddg_node opprB addrA subrK. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq path) mathcomp(div choice order ssralg ssrnum ssrint intdiv) fourcolor(hypermap)