We proved that all the usual things are equivalent to the axiom of choice: Zorn’s lemma, the well ordering principle, cardinal comparability (given two sets, one must inject into the other), and the ...

every family of well ordered sets has a least member — informally, “the well ordered sets are well ordered”; ...

Thurston gave a concrete procedure to construct triangulations of the 2-sphere where 5 or 6 triangles meet at each vertex. How can you get the icosahedron using this procedure? Gerard Westendorp has a ...

Earlier this month the Mathematics Institute at Uppsala University hosted a conference called Categorification in Algebra and Topology, clearly a theme close to our collective heart. As yet there are ...

Nov 11, 2024 20:33 Going back and rereading Tom’s old post, what Tom wrote about there amounted to working with a finite parameter set ...

Sep 18, 2018 Tai-Danae Bradley has a new booklet on applied category theory.

May 31, 2011 The relationships between Euler characteristic and different kinds of Möbius inversion. This Week’s Finds in Mathematical Physics (Week 295) Apr 17, 2010 In “week295” of This Week’s Finds ...

Oct 9, 2007 On weak Lie n-algebras, differential graded Clifford algebra and Roytenberg’s work on weak Lie 2-algebras.

Nov 7, 2024 00:45 Here’s a way to argue that Gerard’s solution to my puzzle is correct. Thurston showed that any star of the ...

Previously: Part 5. Next: Part 7. A category theorist might imagine that a chapter with this title would be about constructing colimits, and they’d be half right.