[Heather] and her sister [Annie] went out to lunch with [Heather]'s sister [Rebecca]. [Heather] asked her two sisters [Cheryl] and [Annie] if they were free for coffee this coming weekend.
('Rebecca', 'Cheryl')
[Heather] and her sister [Annie] went out to lunch with [Heather]'s sister [Rebecca]. [Heather] asked her two sisters [Cheryl] and [Annie] if they were free for coffee this coming weekend.
[{('Rebecca', 'sister', 'Cheryl'): [('Rebecca', 'sister', 'Annie'), ('Annie', 'sister', 'Cheryl')]}, {('Rebecca', 'sister', 'Annie'): [('Rebecca', 'sister', 'Heather'), ('Heather', 'sister', 'Annie')]}, {('Annie', 'sister', 'Cheryl'): [('Annie', 'sister', 'Heather'), ('Heather', 'sister', 'Cheryl')]}]
['sister', 'sister', 'sister', 'sister']