code: def remove(self, element, multiplicity=None):
          _elements = self._elements
          if element not in _elements:
              raise KeyError
          old_multiplicity = _elements.get(element, 0)
          if multiplicity is None or multiplicity >= old_multiplicity:
              del _elements[element]
              self._total -= old_multiplicity
          elif multiplicity < 0:
              raise ValueError("Multiplicity must be not be negative")
          elif multiplicity > 0:
              _elements[element] -= multiplicity
              self._total -= multiplicity
          return old_multiplicity