Proofs from THE BOOK

Dedicated to the memory of Paul Erdos, Martin Aigner and Gunter M. Ziegler's book (with the Subject title) offers examples of proofs with "brilliant ideas, clever insights and wonderful observations." They include chapters on Number Theory, Geometry, Analysis, Combinatorics, and Graph Theory. My question is, what would likely be included if there were a chapter on Category Theory? Ellis D. Cooper [For admin and other information see: http://www.mta.ca/~cat-dist/ ]