Question: when do white walkers appear in game of thrones
[{'answer': 'Oathkeeper', 'provenance': [{'wikipedia_id': '5424539', 'title': 'White Walker', 'start_paragraph_id': 17, 'start_character': 424, 'end_paragraph_id': 17, 'end_character': 434, 'bleu_score': 1.0, 'section': 'Section::::TV adaptation.\n'}]}, {'provenance': [{'wikipedia_id': '5424539', 'title': 'White Walker', 'start_paragraph_id': 17, 'start_character': 37, 'end_paragraph_id': 17, 'end_character': 790, 'bleu_score': 0.859699928643852, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 8777093042870502596}, 'section': 'Section::::TV adaptation.\n'}]}]