[Annie] took her younger sister [Heather] to the carnival last weekend. [Cheryl] is taking a trip to see her sister [Rebecca]. [Heather] is taking a trip to see her sister [Cheryl]. [Heather] and her sister [Annie] were getting together this weekend so that they could go hiking together they had n't spent time together alone in a while.
('Heather', 'Rebecca')
[Annie] took her younger sister [Heather] to the carnival last weekend. [Heather] and her sister [Annie] were getting together this weekend so that they could go hiking together they had n't spent time together alone in a while. [Heather] is taking a trip to see her sister [Cheryl]. [Cheryl] is taking a trip to see her sister [Rebecca].
[{('Heather', 'sister', 'Rebecca'): [('Heather', 'sister', 'Annie'), ('Annie', 'sister', 'Rebecca')]}, {('Annie', 'sister', 'Rebecca'): [('Annie', 'sister', 'Cheryl'), ('Cheryl', 'sister', 'Rebecca')]}, {('Annie', 'sister', 'Cheryl'): [('Annie', 'sister', 'Heather'), ('Heather', 'sister', 'Cheryl')]}]
['sister', 'sister', 'sister', 'sister']