proposition: Lemma dvdr_sub a b c : a %| b -> a %| c -> a %| b - c.
proof: Proof. by move=> ab ac; rewrite dvdr_add // dvdrN. Qed.
imports: HB(structures) Coq(ssreflect ssrfun ssrbool Arith.Wf_nat) mathcomp(eqtype ssrnat div seq path) mathcomp(ssralg fintype perm tuple choice generic_quotient) mathcomp(matrix bigop zmodp mxalgebra poly) stronglydiscrete