proposition: Lemma kerK m n (M : 'M[R]_(m,n)) : ker M *m M = 0.
proof: Proof. rewrite -row_matrixP => i; rewrite row_mul row0. by apply/eqP/kerP_subproof; exists (delta_mx 0 i); rewrite rowE. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq path) mathcomp(ssralg fintype perm choice matrix bigop zmodp mxalgebra poly) ssrcomplements dvdring stronglydiscrete