[Dennis] asked his father [Nicholas] if they could go to the library. [Nicholas]'s father [Clarence] was there already, waiting for them.
('Dennis', 'Clarence')
[Dennis] asked his father [Nicholas] if they could go to the library. [Nicholas]'s father [Clarence] was there already, waiting for them.
[{('Dennis', 'grandfather', 'Clarence'): [('Dennis', 'father', 'Nicholas'), ('Nicholas', 'father', 'Clarence')]}]
['father', 'father']