I take a lot of flak on this one, but I have done my homework. For a quick introduction, see: https://www.youtube.com/watch?v=DmFTgeK7U6U I also recommend: https://www.youtube.com/watch?v=h5i_iDyUTCg I then refer you to: http://bit.ly/1OGfioT (see books below also). Original video: https://www.youtube.com/watch?v=ZP8QfiE9sxo