proposition: Lemma rectC_mull x y z : z * (x + 'i * y) = z * x + 'i * (z * y).
proof: Proof. by rewrite mulrDr mulrCA. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(ssrAC div fintype path bigop order finset fingroup) mathcomp(ssralg poly)