Pieces which have more than 1 composer.

[coulonnus]

Do I have to add the piece at each Composer page?

[Carolus]

No. If the work has two composers, Creative the page under one composer (hopefully the one best known for the piece) and include in the second composer's category by including [[Category:Lastname, Firstname|Work title]] beneath the comments section at the very bottom (in the edit window). If there are more than two composers involved the item needs to go under (Various).

[coulonnus]

I did this for this page: http://imslp.org/wiki/Grosse_theoretisch-praktische_Klavierschule_%28Lebert,_Sigmund%29. Note that I created the
http://imslp.org/wiki/Category:Stark,_Ludwig afterwards. Please check.