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* Which is the simplest example?
@ 2001-02-16 13:43 Peter Freyd
  2001-02-16 18:18 ` Danilov Nikita
  0 siblings, 1 reply; 2+ messages in thread
From: Peter Freyd @ 2001-02-16 13:43 UTC (permalink / raw)
  To: categories

I said that the simplest example of a category with pullbacks but not
products is the discrete category with two objects. Come to think of
it, any category with exactly two morphisms is an example.



^ permalink raw reply	[flat|nested] 2+ messages in thread

* Re: Which is the simplest example?
  2001-02-16 13:43 Which is the simplest example? Peter Freyd
@ 2001-02-16 18:18 ` Danilov Nikita
  0 siblings, 0 replies; 2+ messages in thread
From: Danilov Nikita @ 2001-02-16 18:18 UTC (permalink / raw)
  To: categories

Peter Freyd writes:
 > I said that the simplest example of a category with pullbacks but not
 > products is the discrete category with two objects. Come to think of
 > it, any category with exactly two morphisms is an example.

Initial question was

	  If a category C has pullbacs no terminal object, then has C finite
	  product?

Now, think of empty category (one without objects and morphisms):

(*) it doesn't contain terminal object
(*) it does have pullbacks of all pairs of objects (because there are none)
(*) it doesn't contain all finite products (as it doesn't contain limit
of empty diagram---terminal object)

Now, simplify _this_ counter-example. :)

Actually, if terminal object is considered as product of zero multipliers
(as it's usually does), then initial question contains answer in itself.

Nikita.



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