proposition: Lemma gnode4 d : gnode (gnode (gnode (gnode d))) = d.
proof: Proof. by apply/(addIr (- Gpoint 1 1)); rewrite !gnode_sub1 gface4. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq path) mathcomp(div choice order ssralg ssrnum ssrint intdiv) fourcolor(hypermap)