story: [Mark] called his brother [Peter] on the phone. He wanted to go out for some beers. [Michelle] and [Erik] went to the park with their father, [Peter]. [Peter]'s mother, [Sandra], stayed at home preparing tea.
query: ('Erik', 'Sandra')
clean_story: [Michelle] and [Erik] went to the park with their father, [Peter]. [Peter]'s mother, [Sandra], stayed at home preparing tea.
proof_state: [{('Erik', 'grandmother', 'Sandra'): [('Erik', 'father', 'Peter'), ('Peter', 'mother', 'Sandra')]}, {('Erik', 'father', 'Peter'): [('Erik', 'sister', 'Michelle'), ('Michelle', 'father', 'Peter')]}]