The proof of Proposition 2.7.1 on page 59 in Volume I of "Handbook of Categorical Algebra" by Francis Borceux may be a candidate. John Gray once told me that the proof is due to Peter Freyd. When I was studying category theory in graduate school, proofs of this proposition, the Adjoint Functor Theorem, and some other results in "Categories, Allegories" struck me as demonstrating a creative, original, and insightful use of limits and colimits. Best wishes, Ralph Wojtowicz Metron, Inc. 1818 Library Street, Suite 600 Reston, VA 20190 On Wed, 24 Jun 2009, Ellis D. Cooper wrote:
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
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