"Thema en Variatie / Theme and Variation" for cello solo is a real ´contemporary´ piece (oops).
The theme is simple (later reused in the 2nd StringQuartet), the variations are not.
As a mather of fact the variations are quite far-fetched (the ´contemporary´ part of the piece): independant of the right hand that handles the bow, the left hand moves between distinctive positions above the neck, this position is indicated with a seperate staff.
At the same time the left hand still has to push the strings on the neck determined by the written notes.
The impossibility of playing the prescribed notes while maintaining the prescribed left handposition (which is leading) forces the instrumentalist to the play notes ´as exactly´ as possible.
There are some 6 variations, each variation becomes more difficult than the last, until in the last variation the theme hardly will be recognizable.
"Thema en Variatie / Theme and Variation" is available in two version´s: the first for cello solo, the second for two cello´s unisono, as the composer thinks it´s nice to hear the differences in pitches that will originate during the performance.