code: def remove(self, key):
          '''Returns a new ImmutableDict with the given key removed.'''
          copydict = ImmutableDict()
          copydict.tree = self.tree.remove(hash(key))
          copydict._length = self._length - 1
          return copydicf remove(self, key):
          '''Returns a new ImmutableDict with the given key removed.'''
          copydict = ImmutableDict()
          copydict.tree = self.tree.remove(hash(key))
          copydict._length = self._length - 1
          return copydict
docs: Returns a new ImmutableDict with the given key removed.