You start with wikipedia, e.g. http://en.wikipedia.org/wiki/Permutation

The question is how exactly are guys like Munger and Buffet using this to choose stock. I'm missing some obvious link apparently.

If you start thinking about investments by incorporating decision trees, I think you will start inverting and questioning the potential investment when it comes down to whether or not you should act. This is really helpful to get yourself in the mindset to look at downside risk and evaluate an investment from all angles.

Yeah, but where do permutations and combinations come in? I don't see it at all.