I was reading a paper on the computability of AIXI  and came across the notion of $\Sigma^0_n$-computability for real-valued functions in section 2.3.
I'd like to read about this in more detail. Unfortunately I couldn't find this definition anywhere else in the literature. I already checked the references given at the end of the paper.
Could somebody point me to some book/article I can take a look at?
- On the Computability of AIXI by J. Leike and M. Hutter (2015)