Question: what was the purpose of a customs union
[{'answer': 'increasing economic efficiency', 'provenance': [{'wikipedia_id': '5864', 'title': 'Customs union', 'start_paragraph_id': 2, 'start_character': 59, 'end_paragraph_id': 2, 'end_character': 89, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'answer': 'establishing closer political and cultural ties between the member countries'}, {'provenance': [{'wikipedia_id': '5864', 'title': 'Customs union', 'start_paragraph_id': 2, 'start_character': 0, 'end_paragraph_id': 2, 'end_character': 170, 'bleu_score': 0.910879922930628, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 4762198400391483952}, 'section': 'Section::::Abstract.'}]}]