There's a passage approximately two minutes before the main fugue theme of the fourth mvt. in Beethoven's Hammerklavier op. 106; it lays out a brilliant theme for a fugue which is thereafter never heard again! It comes out of nowhere and then disappears just as you are getting into it. It can be heard here (go to ~39:25) - the whole thing only lasts 12 seconds!
My question is this: Has anyone (including Beethoven himself) ever used this theme in any other context? It just seem to good to not develop into a full-fledged fugue. Any other information regarding this passage (other examples of great themes that are only briefly heard included) would be greatly appreciated!
Also, please do let me know if this question would be better suited for SE Music Fans; if so, I will move it.