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1. Section “Necessity of naturality” sounded like there is nothing interesting going on if we look at the unnatural isomorphism of hom-sets. But this isn’t the case, already in the 60s a graph-theoretical and purely categorical facts of this form have been established. I’m adding the two earliest references.

Tomas Jakl

• CommentRowNumber102.
• CommentAuthorUrs
• CommentTimeJun 18th 2021
• (edited Jun 18th 2021)

The entry fell short of really citing the following in full, so I have added it now:

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