private static void verifyProperty1(Node<?> n) {
    if (n == null) return;
    assert n.getParent() != n;
    assert n.getLeft() != n;
    assert n.getRight() != n;
    assertParentChild(n);

    verifyProperty1(n.getLeft());
    verifyProperty1(n.getRight());
  }
private static void verifyProperty1(Node<?> n)