proposition: Lemma leqifD_dist n1 n2 n3 : `|n1 - n3| <= `|n1 - n2| + `|n2 - n3| ?= iff (n1 <= n2 <= n3) || (n3 <= n2 <= n1).
proof: Proof. exact: leqifD_distz. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(fintype finfun bigop order ssralg countalg ssrnum) mathcomp(poly)