Wolfgang Amadeus Mozart's Piano Sonata No. 9 in D major, K. 311 / 284c, was written on the composer's stay in Augsburg and Mannheim in November-December 1777, and is contemporaneous with his Sonata K. 309. The three sonatas K. 309–311 were published as a set 'Opus IV' in about 1782, by Franz Joseph Heina in Paris.
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