fact: Variable ker_col : forall m (M : 'cV[R]_m), 'M[R]_(dim_ker_col M,m).
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