proposition: Lemma imp_trans4 P Q R S: (P -> Q) -> (R -> S) -> (Q -> R) -> P -> S.
proof: Proof. move=>H1 H2 H3. move=>p; move: (H1 p). Undo. move/H1. by move/H3 /H2. Qed.
imports: mathcomp(ssreflect ssrfun eqtype ssrnat ssrbool prime eqtype)