It is not known when Mozart completed his Concerto for Two Pianos and Orchestra in E-flat major, K. 365/316a, but research by Alan Tyson shows that cadenzas for the first and third movements are written in his and his father's handwriting on a type of paper used between August 1775 and January 1777. However, most sources, including Alan Tyson's book Mozart: Studies of the Autograph Scores or more recently Lindeman's The Concerto: A Research and Information Guide (2006) indicate that it was composed in 1779. It is presumed that Mozart wrote it to play with his sister Maria Anna ("Nannerl"). Years later he performed it in a private concert with pupil Josepha Barbara Auernhammer.
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