docs: def find_prekeyed(self, value, key):
          """
          Find a value in a node, using a key function. The value is already a
          key.
          """
  
          while self is not NULL:
              direction = cmp(value, key(self.value))
              if direction < 0:
                  self = self.left
              elif direction > 0:
                  self = self.right
              elif direction == 0:
                  return self.value