Question: when was free movement in the eu introduced
[{'answer': '1957', 'provenance': [{'wikipedia_id': '4051041', 'title': 'Freedom of movement for workers in the European Union', 'start_paragraph_id': 4, 'start_character': 171, 'end_paragraph_id': 4, 'end_character': 175, 'bleu_score': 1.0, 'section': 'Section::::History.\n'}]}, {'provenance': [{'wikipedia_id': '4051041', 'title': 'Freedom of movement for workers in the European Union', 'start_paragraph_id': 4, 'start_character': 0, 'end_paragraph_id': 4, 'end_character': 591, 'bleu_score': 0.7591455917927521, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 16299035994697908017}, 'section': 'Section::::History.\n'}]}]