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