A personal knowledge management process.
The core of the process revolves around two collections of notes - Reference Notes which summarise source material and include a link to the source, and the collection of evergreen notes which are written in the interpretive part of the process.
The 20th-century German sociologist Niklas Luhmann managed to publish 70 books. He credits much of his success to his Zettelkasten, or "slip box."
_Luhmann, N. (1992). Communicating with Slip Boxes. In A. Kieserling (Ed.), & M. Kuehn (Trans.), Universität als Milieu: Kleine Schriften (pp. 53–61). page 
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see also Zettelkasten project