Max Reger and Karl Straube together added a 3rd subject to the "2-stig. Inventionen" by JSB as a "School for Trio-Playing"
(sorry for my English...)
The right hand is like the piano-score, The left hand is played by the pedals. For the now free left hand they added an own part.
(II): Rfl8/O4 (left)
(I): Bd8/O4/Nas/Tz (right)