proposition: Lemma poset_trans (y x z : T) : x <== y -> y <== z -> x <== z.
proof: Proof. by case: T y x z=>S [[l b B R A Tr]] ? x y z; apply: (Tr). Qed.
imports: mathcomp(ssreflect ssrbool ssrfun ssrnat eqtype seq) pcm(options axioms pred prelude)