therest

def is_correct_rb_tree(tree):
    if tree.root is None:
        return True

    if tree.root.color is not Colors.black:
        return False

    if black_height(tree.root) == 0:
        return False

    return check_children(tree.root)

def check_children(node):
    if node is None:
        return True

    if node.color is Colors.red:
        color_left = Colors.black
        if node.left is not None:
            color_left = node.left.color
        color_right = Colors.black
        if node.right is not None:
            color_right = node.right.color
        return color_left is Colors.black and color_right is Colors.black and check_children(node.left) and check_children(node.right)
    else:
        return check_children(node.left) and check_children(node.right)

def black_height(node):
    if node is None:
        return 1

    left_height = black_height(node.left)
    if left_height is 0:
        return 0

    right_height = black_height(node.right)
    if right_height is 0:
        return 0

    if left_height != right_height:
        return 0
    else:
        val = left_height
        if node.color is Colors.black:
            val += 1
        return val