In this Fugue from “The Art of the Fugue“, Bach shows us what he can do with a theoretical countersubject. It’s theoretical because he starts the piece without the presence of the actual subject known so well from the rest of the book. Then, he introduces this real subject (in sustained half notes — see [...]

Just a three-voiced fugue based on “Shave and a Haircut, Two Bits. ” I wrote it for recorder trio but it can be played on pretty much anything.
The Haircut Fugue, 2005 Midi PDF