[John] and his sister [April] went to brunch today at the new diner. [Janet] and her brother [John] sat down together to clip coupons.
('April', 'Janet')
[John] and his sister [April] went to brunch today at the new diner. [Janet] and her brother [John] sat down together to clip coupons.
[{('April', 'sister', 'Janet'): [('April', 'brother', 'John'), ('John', 'sister', 'Janet')]}]
['brother', 'sister']