proposition: Lemma matchpg_etrace et w : matchpg Bstack0 (etrace et) w = matchpg Bstack0 et w.
proof: Proof. rewrite /etrace /etrace_perm. case: (even_trace et) => /=; first by rewrite permt_id. rewrite -[Bstack0]/(stack_of_bitseq [::]) -{1}[[::]]/(map negb [::]). elim: et [::] w => [|e et IHet] lb [|s w] //. by case: e (IHet (cbit0 e :: lb) w); case: s => //=; case: lb => [|[]] //=. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype) fourcolor(color)