[Robert] was playing catch with his son, [Ronald]. [Lizzie] imitated her brother throwing the ball back and forth. [Marie] read her son [Mario] a bedtime story every night. [Robert] was waiting to meet his wife, [Marie], at the airport whose flight was delayed by two hours.
('Lizzie', 'Mario')
[Robert] was playing catch with his son, [Ronald]. [Lizzie] imitated her brother throwing the ball back and forth. [Robert] was waiting to meet his wife, [Marie], at the airport whose flight was delayed by two hours. [Marie] read her son [Mario] a bedtime story every night.
[{('Lizzie', 'brother', 'Mario'): [('Lizzie', 'brother', 'Ronald'), ('Ronald', 'brother', 'Mario')]}, {('Ronald', 'brother', 'Mario'): [('Ronald', 'father', 'Robert'), ('Robert', 'son', 'Mario')]}, {('Robert', 'son', 'Mario'): [('Robert', 'wife', 'Marie'), ('Marie', 'son', 'Mario')]}]
['brother', 'father', 'wife', 'son']