In the last part of the 6th stringquartet, the composer for the first time applied the by the composer invented ´musique-collage´ technique. The score of the first part of W.A.Mozart´s ´dissonance quartet´ was gradually cut in still smaller fragments which literally were rearranged.
In the 9th Stringquartet this technique is further investigated. Fragments become smaller, are turned upside-dowm etcetera etcetera...
Most of the times the compser likes his re-arrangements even more than the original. One of the reasons of course is the comical side-effect of re-arranged well-known pieces. Take e.g. the begining of the 2nd part, Vivaldi´s Spring.
Part 1 re-arranges Beethoven, Brahms & Bártok
Part 2 re-arranges Vivaldi, J.S.Bach & Chopin