proposition: Lemma ImV x : 'Im x^-1 = - 'Im x / `|x| ^+ 2.
proof: Proof. rewrite [x in LHS]Crect invC_rect// ImMr ?(rpredV, rpredD, rpredX)//. by rewrite -mulrN Im_rect ?rpredN// -normC2_rect// -Crect. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(ssrAC div fintype path bigop order finset fingroup) mathcomp(ssralg poly)