Folgezettel is an alphanumeric identification system for the Zettelkasten
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Folgezettel is an alphanumeric identification system for the Zettelkasten. It works by applying a consistent numbering to main notes as they are created, forming initial relationships with other notes. The folgezettel imposes no top down structure on the Zettelkasten, instead it applies relationships between notes which can be followed to build chains of thought.
The alphanumeric system, later dubbed “folgezettel” or “follow-up note,” allowed Luhmann to work non-hierarchically. Ideas were no longer bound to topics, listed alphabetically, or cataloged according to consecutive prime numbers only, all of which would have created a linearly organized system. By employing combinations of numbers and letters, Luhmann was able to place notes in between one another, allowing ideas to branch off in any direction.[1, pp. 79–80]