What's the difference between a computer and a rock?
Author’s note: I wrote this in 2017 and it languished in the drafts since then because I couldn’t think of a good conclusion. Really this is typical of the subject matter and all this piece offers is something to chew on, if you have the interest in it or have never before considered the question. At the time I was helping tutor a TLA⁺ seminar and had the opportunity to ask Leslie Lamport (who has thought about computation quite a bit!
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