proposition: Lemma halfg_add_odd d : halfg (d + oddg d) = end0g d.
proof: Proof. by rewrite halfg_add halfg_double. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq path) mathcomp(div choice order ssralg ssrnum ssrint intdiv) fourcolor(hypermap)