Interesting, but I think printed books are much better for learning, e.g. <a href="http:&#x2F;&#x2F;noBSgui.de&#x2F;to&#x2F;MATHandPHYSICS&#x2F;" rel="nofollow">http:&#x2F;&#x2F;noBSgui.de&#x2F;to&#x2F;MATHandPHYSICS&#x2F;</a> (disclaimer: I am the author)