Mark finds a bridge (Mimi calls it 'Arch' form) structure (ABCBA) in
Bartoks fourth string quartet.  This I belive is one of Bartoks "tricks"
of the trade, I first noticied it in his 'music for strings.  Percussion
and Celesta', and since in many other of his works, acctuly in many other
composers works as well, the compositional trait ABC, turning backwards
mid C and going BA ending up where You started has been used since the
Renaissance.  (some might complain that its not a perfect arch (like in
the suggsted quartet), well; this is theoretical stuff, any prospering
composer would as such, let the music grow around it..)

cheers
peter lundin