proposition: Lemma inj_sewd : injective sewd.
proof: Proof. by move=> xd yd /eqP; rewrite /= eq_Tagged => /eqP. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype path fingraph) fourcolor(hypermap geometry color patch)