A "slip box contains 4x6 index cards with only two note types: Source Notes and Main Notes",
where Main Notes use "Luhmann's alphanumeric numbering" 0b.
The digital part contains two text files: "one to list Sources, and a 'Card List' to list main cards as Einsteigspunkte (entry points) to the slip box", where he "will add keywords to a card title" as a keyword index. 0c2a
This hybird system allows he to "leverage digital to search quickly for a source or card location, but keep the fun of taking and making notes on paper".