I am returning to this for the second time, originally having learnt it two years ago. The Prelude is a 3 part invention, the plaintive opening theme in the top voice appearing seven times in the first nine bars. The Fugue has two distinct countersubjects, leading to an intricate triple counterpoint. One of the challenges of playing this is bringing out the initial subject when it appears in the lowest voice, with the upper 3 voices all at different stages of subject, or countersubject. It’s why I love playing Bach, listening to how the parts follow and respond to each other, and the different character of each part depending on which register of the piano it uses.