In mathematics, the category number of a mathematician is a humorous construct invented by Dan Freed,   intended to measure the capacity of that mathematician to stomach the use of higher categories. It is defined as the largest number n such that he or she can think about n-categories for a half hour without getting a splitting headache.
- Freed, Dan (2001). "The Verlinde Algebra is Twisted Equivariant K-Theory". Turkish Journal of Mathematics. 25 (1): 159–167.
- Freed, Dan. "Remarks on Chern-Simons Theory" (PDF). Retrieved 8 August 2016.
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