From www.mutopiaproject.org

The Inventions and Sinfonias, BWV 772–801, also known as the Two- and Three-Part Inventions, are a collection of thirty short keyboard compositions by Johann Sebastian Bach (1685–1750): 15 inventions, which are two-part contrapuntal pieces, and 15 sinfonias, which are three-part contrapuntal pieces. They were originally written as "Praeambula" and "Fantasiae" in the Klavierbüchlein für Wilhelm Friedemann Bach, a Clavier-booklet for his eldest son, and later rewritten as musical exercises for his students.
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