[George] made a sandwich for his son [Douglas]. [Douglas]'s brother [John] ate an apple instead.
('George', 'John')
[George] made a sandwich for his son [Douglas]. [Douglas]'s brother [John] ate an apple instead.
[{('George', 'son', 'John'): [('George', 'son', 'Douglas'), ('Douglas', 'brother', 'John')]}]
['son', 'brother']