proposition: Lemma dvdr_addl a b c : b %| a -> (b %| c + a) = (b %| c).
proof: Proof. move=> ba; apply/idP/idP=> ha; last exact: dvdr_add. by rewrite -[c](addrK a) dvdr_sub. 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