SwapCols(ref M: MAT, i: INT, j: INT)
/**/ M := StdDegLexMat(5); /**/ SwapCols(ref M, 1,5); /**/ M; matrix(QQ, [[1, 1, 1, 1, 1], [0, 0, 0, 0, 1], [0, 1, 0, 0, 0], [0, 0, 1, 0, 0], [0, 0, 0, 1, 0]])