Arguably, “natural equivalence” is just the particular case of equivalence where the objects you’re talking about are functors.

]]>I have edited the text at *natural equivalence* a little more.

I changed the ‘general theory’ sentence at equivalence.

]]>Hm, but a natural equivalence is just an equivalence between functors. Need not be 1-functors or 2-functors. Could be $\infty$-functors.

]]>If equivalence is treated so generally, couldn’t natural equivalence too, or is its restriction to 2-categories of 2-functors been determined by use? But then what is the general notion of ’naturalness’ as applied to equivalences in general to be called? And how is it defined? This relates to a question I posed to Mike.

While I’m on this subject,

The general theory of equivalence is discussed at equivalence relation…

Is it? It seems to be a rather limited notion of equivalence discussed there.

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