proposition: Lemma gcdr_addr_l a b c : b %| c -> gcdr (a + c) b %= gcdr a b.
proof: Proof. move=> Hbc. by rewrite (eqd_trans (gcdrC _ _)) ?(eqd_trans (gcdr_addr_r _ _)). 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