proposition: Lemma gcdrA a b c : gcdr a (gcdr b c) %= gcdr (gcdr a b) c.
proof: Proof. rewrite /eqd !dvdr_gcd !dvdr_gcdl !dvdr_gcdr. do 2!rewrite (dvdr_trans (dvdr_gcdr _ _)) //. by do 2!rewrite (dvdr_trans (dvdr_gcdl _ _)) //. 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