Classical logic up to Goedel's theorem.
Fairly standard Bayesian probability.
A little bit of coding (up to Kraft's inequality).
Computability and algorithmic complexity.
Solomonoff induction.
It's all pretty basic stuff, but taken from a variety of disciplines.
Just a quick question, does anyone know which math topics I'd have to learn to understand the work on AIXI and the Gödel machine? Any pointers or suggestions would be appreciated.