def METHOD_NAME():
    from pymbolic.primitives import Variable
    arg_dict = {
            "m": 3*Variable("nx"),
            "n": 2*Variable("ny")+4}
    space = isl.Set("[nx, ny, nz] -> { []: }").params().space
    poly = isl.PwAff("[m, n] -> { [3 * m + 2 * n] : "
        "m > 0 and n > 0; [7* m + 4*n] : m > 0 and n <= 0 }")
    from loopy.isl_helpers import subst_into_pwaff
    result = subst_into_pwaff(space, poly, arg_dict)
    expected = isl.PwAff("[nx, ny, nz] -> { [(9nx + 4ny+8)] : nx > 0 and ny > -2;"
            " [(21nx + 8ny+16)] : nx > 0 and ny <= -2 }")
    assert result == expected