>>> {Distance(12): 1}
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unhashable type: 'Distance'

>>> 5 * Distance(kilometers=6)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for *: 'int' and 'Distance'
>>> Distance(kilometers=6) // 5
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for //: 'Distance' and 'int'