[Clarence] is taking is son [Nicholas] out for a weekend camping trip. [Nicholas]'s son [Dennis] is sick and can not go.
('Dennis', 'Clarence')
[Clarence] is taking is son [Nicholas] out for a weekend camping trip. [Nicholas]'s son [Dennis] is sick and can not go.
[{('Dennis', 'grandfather', 'Clarence'): [('Dennis', 'father', 'Nicholas'), ('Nicholas', 'father', 'Clarence')]}]
['father', 'father']