I have lecture notes that I'd like to turn into a book one day. I have not yet had time to adapt to my new TeX system, and the drawings done via ps-tricks do not yet come out as planned. In addition, there are gaps and mistakes that I have not yet had time to fill and correct (the chapter on composition should be essentially correct and complete, however). In any case, the present set of notes, for the time being, can be found
<a href="http://www.rzuser.uni-heidelberg.de/~hb3/publ/bf.pdf">here</a>. Comments and
corrections are welcome.