proposition: Theorem cltSleP n: natp n -> forall a, (a <c (csucc n) <-> a <=c n).
proof: Proof. move => nN a. apply:(iff_trans (NltP (NS_succ nN) a) (iff_sym (NleP nN a))). Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat)