proposition: Lemma memberP n (x : R) (I : 'cV[R]_n) : reflect (exists J, x%:M = J *m I) (member x I).
proof: Proof. case: member_specP => /= [J ->|h]; constructor; first by exists J. by case=> J hJ; move: (h J); rewrite hJ eqxx. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq path) mathcomp(ssralg fintype perm choice fingroup) mathcomp(matrix bigop zmodp mxalgebra poly) ssrcomplements