proposition: Lemma cdiff_lt_symmetry n p: natp p -> n <c p -> cpred (p -c n) <c p.
proof: Proof. move=> pN ltnp; exact:(cdiff_lt_symmetry' n pN (card_gt_ne0 ltnp)). Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat) mathcomp(binomial div)