proposition: Lemma lt_trans : transitive Rlt.
proof: Proof. move=> y x z le_xy le_yz. by rewrite -subr_gt0 -(subrK y z) -addrA addr_gt0 // subr_gt0. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(ssrAC div fintype path bigop order finset fingroup) mathcomp(ssralg poly)