[Clarence] wanted his son, [Nicholas], to go fishing with him. [Dennis] asked his father, [Nicholas], to help him with his math homework. [Nicholas] could n't, because he was lousy at math himself.
('Dennis', 'Clarence')
[Dennis] asked his father, [Nicholas], to help him with his math homework. [Nicholas] could n't, because he was lousy at math himself. [Clarence] wanted his son, [Nicholas], to go fishing with him.
[{('Dennis', 'grandfather', 'Clarence'): [('Dennis', 'father', 'Nicholas'), ('Nicholas', 'father', 'Clarence')]}]
['father', 'father']