code: private Node<T> moveRedLeft(Node<T> h) {
          // assert (h != null);
          // assert isRed(h) && !isRed(h.left) && !isRed(h.left.left);
  
          flipColors(h);
          if (h.right.left != null && h.right.left.red) { 
              h.right = rotateRight(h.right);
              h = rotateLeft(h);
              flipColors(h);
          }
          return h;
      }
docs: are black, make h.left or one of its children red.