Talk:Diagram (category theory)
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[edit] Variance of a diagram
Is a "functor" here necessarily a covariant functor? Stephan Spahn (talk) 20:06, 28 May 2011 (UTC)
- Hi Stephan, this is a strange question. A functor is a functor. To say "a contravariant functor from C to D" is an elaborate way to say "a functor from Cop to D". Nobody should ever use the notation F:C→D to mean F:Cop→D. Occasionally someone might use the phrase "covariant functor" if they want to emphasize the point, but it is not necessary to say covariant at all.
- I don't think that your addition of (covariant) is necessary here, but we can leave it for a few days in case anyone else has a strong opinion. ComputScientist (talk) 10:16, 30 May 2011 (UTC)
[edit] Accessibility
The article would be more accessible to interested amateurs if it offered some motivations or intuitions for the notions of "diagram" and "cone". I'm not asking for the historical reasons for these terms, just an indication of why these terms might suggest themselves for, or partly describe, the relevant notions of category theory. yoyo (talk) 22:13, 23 December 2011 (UTC)
