google translate:
The world of Niklas Luhmann – Schmidt now sometimes finds it on the back of the slip. Because Luhmann apparently recycled every scrap of paper he could find for his box. So it can happen that on the front of the note there are condensed reflections on the concept of autopoiesis or summaries of unknown treatises from earlier centuries, while on the back you can find the first arithmetic exercises by Luhmann's children. Or check statements. Or instructions to the household help: “Sweep and wipe the basement stairs thoroughly”, for example.
Luhmann adhered to the standard advice to write only on one side of his cards, though perhaps not just for the usual reasons, but in part because he recycled the papers he had at hand to make his slips. On the backs of his notes one can find instructions he'd made to his household help, his children's homework papers, bank statements, and other papers he happened to have at hand.