def test_singleton():
 AreEqual((frozenset([]) is frozenset([])), True)
 x = frozenset([1, 2, 3])
 AreEqual((x is frozenset(x)), True)

def test_singleton ( ) : AreEqual ( ( frozenset ( [ ] ) is frozenset ( [ ] ) ) , True ) x = frozenset ( [ 1 , 2 , 3 ] ) AreEqual ( ( x is frozenset ( x ) ) , True )
verify that an empty frozenset is a singleton .