Question: who has won the mens singles title in the australian open tennis tournament
[{'answer': 'Roger Federer', 'provenance': [{'wikipedia_id': '55901829', 'title': "2018 Australian Open – Men's Singles", 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 13, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '55901829', 'title': "2018 Australian Open  Men's Singles", 'section': 'Section::::Abstract.', 'start_paragraph_id': 1, 'end_paragraph_id': 1, 'meta': {'evidence_span': ["Roger Federer successfully defended his title, defeating Marin Čilić in the final, 62, 67, 63, 36, 61 to win the Men's Singles tennis title at the 2018 Australian Open", "oger Federer successfully defended his title, defeating Marin Čilić in the final, 62, 67, 63, 36, 61 to win the Men's Singles tennis title at the 2018 Australian Open. It was Federer's 20th Grand Slam singles title and, at the time, record-equalling sixth Australian Open men's singles title (tied with Roy Emerson and Novak Djokovic).", "Roger Federer successfully defended his title, defeating Marin Čilić in the final, 62, 67, 63, 36, 61 to win the Men's Singles tennis title at the 2018 Australian Open. It was Federer's 20th Grand Slam singles title and, at the time, record-equalling sixth Australian Open men's singles title (tied with Roy Emerson and Novak Djokovic)."]}}]}, {'provenance': [{'wikipedia_id': '23456108', 'title': "2010 Australian Open  Men's Singles", 'section': 'Section::::Abstract.', 'start_paragraph_id': 1, 'end_paragraph_id': 1, 'meta': {'evidence_span': ["Roger Federer defeated Andy Murray in the final to win the Men's Singles tennis title at the 2010 Australian Open.", "Roger Federer defeated Andy Murray in the final to win the Men's Singles tennis title at the 2010 Australian Open.", "Roger Federer defeated Andy Murray in the final to win the Men's Singles tennis title at the 2010 Australian Open."]}}]}]