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