Bach Prelude and Fugue in D minor

I don’t think I appreciated the complexity of this prelude and fugue when I first played it, as a compulsory piece for the performing component of my A level examination. The prelude keeps up a perpetuum mobile of broken chords in the right hand for the first half accompanied at first by repeated Ds in the left hand which gradually expand to point out the harmony. The 3 part fugue introduces the subject in the top voice and the trill on the third beat of the second bar is integral to the melody, sometimes being shortened to a turn in later iterations of the theme.