proposition: Lemma line_comb_row_eq n m k l a (M: 'M[R]_(n,m)): row k (line_comb k l a M) = row k M + a *: row l M.
proof: Proof. by apply/rowP => i; rewrite !mxE eqxx !mxE. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(ssralg fintype perm choice) mathcomp(matrix bigop zmodp mxalgebra poly mxpoly)