Question: Why is the ethnomusicologist, Bela Viktor Janos Bartok's Piano Concerto No. 2 in G major considered notorious?
{'answer': 'is notorious for being one of the most difficult pieces in the repertoire.', 'supporting_facts': [['Piano Concerto No. 2 (Bartók)', 0], ['Piano Concerto No. 2 (Bartók)', 1], ['Béla Bartók', 0]]}