From www.mutopiaproject.org

The Musical Offering, BWV 1079, is a collection of keyboard canons and fugues and other pieces of music by Johann Sebastian Bach, all based on a single musical theme given to him by Frederick the Great, to whom they are dedicated. The Ricercar a 6, a six-voice fugue which is regarded as the high point of the entire work, was put forward by the musicologist Charles Rosen as the most significant piano composition in history. This ricercar is also occasionally called the Prussian Fugue, a name used by Bach himself. The composition features in the opening section of Douglas Hofstadter's Pulitzer Prize winning book Gödel, Escher, Bach (1979).
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