proposition: Lemma fixedSpacesP f U : reflect {in U, f =1 id} (U <= fixedSpace f)%VS.
proof: Proof. by apply: (iffP subvP) => cUf x /cUf/fixedSpaceP. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype bigop finfun tuple) mathcomp(ssralg matrix mxalgebra zmodp)