....E...........

======================================================================

ERROR: testHash (tester.ProblemTests)

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Traceback (most recent call last):

  File ".../test.py", line 92, in testHash

    self.assertEqual(hash(Interval(3, 11)), hash(Interval(3, 11)))

TypeError: __hash__() should return an int



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Ran 16 tests in 0.006s



FAILED (errors=1)