Bitcoin-related protocol proposals, or analysis or discussion thereof. For example, new P2P messages, new wallet techniques, methods for coinjoins or payment channels, etc.
Try to keep things accessible to developers – so don’t use formal academic terminology that you’d write in a paper, when your could write things more simply.
If you want to use maths, you can use LaTeX (mathjax) markup by surrounding inline formulas with $, for example: $ 1+1=2 $ gives 1+1=2 , or surrounding a standalone block with $$:
1+1=2