I always have trouble deciding whether to start with the genus and drive down to the species or else to start with concrete examples and follow Sisyphus up Mt. Abstraction.
Soon after I made my 3rd try at grad school, this time in Systems Engineering, I was trying to explain sign relations to my advisor and he — being the very model of a modern systems engineer — asked me to give a single simple concrete example, as simple as possible without being trivial, and this is the example I came up with:
Here’s a more compact and self-contained article starting from scratch and covering much of the same material:
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