[Roberto]'s aunt, [Tracy], asked [Roberto] to mow the lawn for her. [Roberto] said he could n't because he had a bad back. [Pedro] took his son, [Roberto], to the library as his sister, [Beverly], waited at home for her brother, [Robert].
('Robert', 'Tracy')
[Pedro] took his son, [Roberto], to the library as his sister, [Beverly], waited at home for her brother, [Robert]. [Roberto]'s aunt, [Tracy], asked [Roberto] to mow the lawn for her. [Roberto] said he could n't because he had a bad back.
[{('Robert', 'sister', 'Tracy'): [('Robert', 'brother', 'Pedro'), ('Pedro', 'sister', 'Tracy')]}, {('Pedro', 'sister', 'Tracy'): [('Pedro', 'son', 'Roberto'), ('Roberto', 'aunt', 'Tracy')]}, {('Robert', 'brother', 'Pedro'): [('Robert', 'sister', 'Beverly'), ('Beverly', 'brother', 'Pedro')]}]
['sister', 'brother', 'son', 'aunt']