In the Zettelkasten (“Slip-box”) every concept would be written on a card as a note with a number to identify it, and every note would be connected to others through a relationship. So basically by following numbers, you create a dialogue with your notes, and so with your brain. And that was on paper. Today I would never do that although maybe on my back you can see something that wanted to reproduce. I would do that with Evernote, or with Notion, and with Readwise. Using my Kindle, I would export all the notes that I’m getting and using a tool, readwise.io, I would get all these interesting pieces of knowledge to come back up to me, in the future.