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