proposition: Remark member_in m x (I : 'cV[R]_m) : (exists i, I i 0 = x) -> member x I.
proof: Proof. by case=> i <-; rewrite memberE subrid. 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