docs: def avl_rotate_double(root, direction):
      """
      Double rotation, either 0 (left) or 1 (right).
  
      Figure:
                      c,1 (right)
                      ----------->
             a              a             c
            /      b,0     /     a,1    /   \
           b       --->   b      -->  b      a
            \            /
             c          c
      """
      other_side = 1 - direction
      root[other_side] = avl_rotate_single(root[other_side], other_side)
      return avl_rotate_single(root, direction)