fact: Definition lfun_preim aT rT (f : 'Hom(aT, rT)) W := (lfun_img (inv_lfun f) (W :&: lfun_img f fullv) + lker f)%VS.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype bigop finfun tuple) mathcomp(ssralg matrix mxalgebra zmodp)