proposition: Lemma DP_lowerK v: (head true v == false) && ends_withT v -> DP_raise (DP_lower v) = v.
proof: Proof. case: v => // a l /= /andP[/eqP -> /eqP]; rewrite /DP_raise. by case:l => // b l /= <-;rewrite - lastI. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype) mathcomp(ssrnat seq path div) mathcomp(fintype tuple finfun bigop finset binomial)