Question: a promise in exchange for a promise is an example of
[{'answer': 'contract', 'provenance': [{'wikipedia_id': '638369', 'title': 'Promise', 'start_paragraph_id': 2, 'start_character': 14, 'end_paragraph_id': 2, 'end_character': 22, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '638369', 'title': 'Promise', 'start_paragraph_id': 2, 'start_character': 0, 'end_paragraph_id': 2, 'end_character': 140, 'bleu_score': 0.9181891462193901, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 7070146372626955648}, 'section': 'Section::::Abstract.'}]}]