[TUHS] Diff: The seminal water we swim in

[Douglas McIlroy <douglas.mcilroy@dartmouth.edu>]

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> this month marks the fiftieth anniversary of the release of what
> would become a seminal, and is arguably the single most important,
> piece of social software ever created.

I'm flattered, but must point out that diff was just one of
a sequence of more capable and robust versions of
proof(1), which Mike Lesk contributed to Unix v3. It, in
turn, copied a program written by Steve Johnson before
Unix and general consciousness of software tools. Credit
must also go to several people who studied and created
algorithms for the "longest common subsequence"
problem: Harold Stone (who invented the diff algorithm
at a blackboard during a one-day visit to Bell Labs), Dan
Hirschberg, Tom Szymanksi, Al Aho, and Jeff Ullman.

For a legal case in which I served as an expert witness,
I found several examples of diff-type programs
developed in the late 1960s specifically for preparing
critical editions of ancient documents. However, Steve
Johnson's unpublished program from the same era
appears to be the first that was inspired as a general
tool, and thus as "social software".

Doug

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