Oddbean new post about login | logout @b4c50e1b I just read your blog post about the "free 2-rig" and schur functors, and I can't help but laugh at the timing. At the end of the post you show that (for a 2-rig R) every natural endofunctor R --> R is a (schur) polynomial, and you compare this to the decategorified case of every natural function R --> R (for a ring R, now) is a polynomial. (Also, I'm sure you know this, but for other readers, in both cases here "natural" is meant in the technical sense of "defined uniformly for all 2-rigs (resp. rings) R") The timing is funny because @c5cf7486 recently posted a blog post of his own working out the decategorified version in detail! And for anyone who hasn't seen them yet, here are the two posts I'm referencing: https://golem.ph.utexas.edu/category/2023/10/the_free_2rig_on_one_object.html https://terrytao.wordpress.com/2023/08/25/yonedas-lemma-as-an-identification-of-form-and-function-the-case-study-of-polynomials/