I was looking through my old copy of "The Devil's DP Dictionary" by Stan Kelly-Bootle, and came across the entry for Stepwise Refinement. I thought "I've seen this before: this is a parody of Darcs patch theory". It included the Null patch, chains of patches, inverse patches, and pseudo-inverse patches. But the book was published in 1981. I've got the pages scanned, but I can't upload them to Wikimedia because they are still in copyright. However I'm quite sure that limited distribution would fall into "fair use" (non-commercial, small part of work, no impact on market, academic relevance). The total file size is about 520kBytes. Assuming people would like to see them, does anyone have any ideas beyond "email to requestors"? Paul.