mathematics free of a blackboard (I. Gelfand and M. Gromov)

[martdowd at aol.com]

 Jose Caballero 

On the other hand, the number 3 in category theory seems to be less dependent on the representation.
 I agree that the natural numbers provide a more fundamental example than the graphs.  For example. Peano arithmetic provides a completely satisfactory formal setting for them, without any reference to sets, and avoids any need for defining them in term of more abstract concepts.  Any set-theoretic definition has a "contrived" flavor, but the von Neumann ordinals also have a certain naturality.

Martin Dowd
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