# reperiendi

## Semantics for the blue calculus

Posted in Category theory, Math, Quantum by Mike Stay on 2011 April 29
 Blue calculus MonCat $\frac{n \mbox{Cob}_2}{}$ 2Hilb Set (as a one object bicategory) Types monoidal categories manifolds 2 Hilbert spaces * Terms with one free variable monoidal functors manifolds with boundary linear functors sets Rewrite rules monoidal natural transformation manifolds with corners linear natural transformations functions Tensor product $\boxtimes$ juxtaposition (disjoint union) tensor product cartesian product $(T | T'):Y$ where $x:X$ is free $([[T]] \otimes_Y [[T']]):X \to Y$ formal sum of cobordisms with boundary from $X$ to $Y$ sum of linear functors disjoint union

In the MonCat column, $\boxtimes$ is the categorified version of the tensor product of monoids.

## Axiom of fun choice

Posted in Fun links, Math by Mike Stay on 2011 April 14

A fun choice function is a function $f$ defined on a collection $J$ of jobs that must be done such that for every job $j \in J, f(j)$ is an element of fun. The axiom of fun choice states,

For any set $\displaystyle J$ of jobs that must be done, there exists a fun choice function defined on $\displaystyle J.$

This axiom asserts that one can always find the fun in any job that must be done; a theorem of Poppins deduces from this that all such jobs are games.

## Monster manual

Posted in Uncategorized by Mike Stay on 2011 April 13

What magical creature lives deep in the earth’s crust and has a horrible lisp? A BATHOLITHK.

## Better than anything 2

Posted in Uncategorized by Mike Stay on 2011 April 1

Better than This Week from Baez,
Better than Lou Kauffman’s knots,
Better than all of the string theory
Witten’s forgot,

Better than Feynman’s graffiti,
Better than Calabi-Yau,
Better than Pauli’s neutrino,
Better than mu and than tau,

Better than Curie, Poincaré,
And Niels and Albert at Solvay
Better than anything except being in love.