In building strategies, It seems like the more Math expertise one has the better. I know that some very successful traders / quants, like Jim Simons for example ( http://www.turtletrader.com/trader-simons.html ) are retired professors, or PhDs. What kinds of topics work well with market study? I've heard Stochastics ( http://en.wikipedia.org/wiki/Stochastic_process ) Econometrics, and Probability Theory. Any other ideas? Any book recommendations here? Thanks!