proposition: Lemma end0g_sub1 d : end0g d - Gpoint 1 1 = halfg (d - Gpoint 1 1).
proof: Proof. by rewrite halfg_add -addrA; case: oddgP. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq path) mathcomp(div choice order ssralg ssrnum ssrint intdiv) fourcolor(hypermap)