proposition: Fact trans : transitive le.
proof: Proof. move=> y x z /andP [hxy /implyP hxy'] /andP [hyz /implyP hyz']. rewrite /le (le_trans hxy) //=; apply/implyP => hzx. by apply/le_trans/hxy'/(le_trans hyz): (hyz' (le_trans hzx hxy)). Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(path fintype tuple bigop finset div prime finfun) mathcomp(finset)