public abstract boolean isNested();
@Test
    void testIsNested() {
        assertThat(Projection.of(new int[] {2, 1}).isNested()).isFalse();
        assertThat(Projection.of(new int[][] {new int[] {1}, new int[] {3}}).isNested()).isFalse();
        assertThat(
                        Projection.of(new int[][] {new int[] {1}, new int[] {1, 2}, new int[] {3}})
                                .isNested())
                .isTrue();
    }