proposition: Lemma subcJ (z : R[i]) : z - z^*%C = 2%:R * (Im z)%:C * 'i%C.
proof: Proof. rewrite ImJ_sub mulrCA mulrA mulfVK ?pnatr_eq0 //. by rewrite -mulrA ['i%C * _]sqr_i mulrN1 opprB. Qed.
imports: HB(structures) mathcomp.ssreflect.ssreflect mathcomp(ssrfun ssrbool eqtype ssrnat seq choice fintype) mathcomp(bigop order ssralg ssrint div ssrnum rat poly closed_field) mathcomp(polyrcf matrix mxalgebra tuple mxpoly zmodp binomial realalg) mathcomp(mxpoly)