For 10 points, name this collection of variations on a theme by King Frederick the Great by J.S. Bach.
One work in this collection has a repeat sign in one voice an extra 16th note later, and has the main theme played in half time by the treble voice while the alto key signature for that part is upside down. In addition to that movement, labeled "a 2 Per motum contrarium," one movement is labeled "Fuga canonica in Epidiapente" despite not having a truly fugal opening, and the main theme in all these works begins with C-E flat-G-A flat-B natural half notes. It has a section labeled "Canones diversi" that include one for 2 violins in unison, and its 6 part ricercare was orchestrated by Anton von Webern. It includes a canone perpetuo and a trio sonata, both for violin, flute, and basso continuo, and is the second to last work in the BWV catalog, preceeding (*) The Art of the Fugue. For 10 points, name this collection of variations on a theme by King Frederick the Great by J.S. Bach.
One work in this collection has a repeat sign in one voice an extra 16th note later, and has the main theme played in half time by the treble voice while the alto key signature for that part is upside down.
The {Musical Offering} [or {Ein Musikalisches Opfer}]