Question: when was the salary cap introduced to the nhl
[{'answer': 'During the Great Depression', 'provenance': [{'wikipedia_id': '23539733', 'title': 'NHL salary cap', 'start_paragraph_id': 4, 'start_character': 51, 'end_paragraph_id': 4, 'end_character': 78, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '23539733', 'title': 'NHL salary cap', 'start_paragraph_id': 4, 'start_character': 0, 'end_paragraph_id': 4, 'end_character': 280, 'bleu_score': 0.8821415355185661, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 15462468197941309431}, 'section': 'Section::::Abstract.'}]}]