[Nancy] invited her sisters, [Theresa] and [Amy], to a party.
('Amy', 'Theresa')
[Nancy] invited her sisters, [Theresa] and [Amy], to a party.
[{('Amy', 'sister', 'Theresa'): [('Amy', 'sister', 'Nancy'), ('Nancy', 'sister', 'Theresa')]}]
['sister', 'sister']