proposition: Lemma leq_BD n p : n - p <= n + p.
proof: Proof. exact:(leq_trans (leq_subr p n) (leq_addr p n)). Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat) mathcomp(seq path fintype div bigop binomial) mathcomp(prime finset ssralg ssrnum ssrint)