fact: Definition line_scale_mx n m k (a: R) (M: 'M[R]_(n,m)) := diag_mx (\row_(i < n) (if i == k then a else 1)) *m M.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(ssralg fintype perm choice) mathcomp(matrix bigop zmodp mxalgebra poly mxpoly)