Hi! I've got a problem with understanding notation in this lecture: http://www.youtube.com/watch?v=FZDy_Dccv4s&feature=BFa&list=PLF4D952FA51A49E66 For example, at 00:44:13, what does all lowercase deltas stand for? He writes: δA=∫(∂L/∂q)δq + (∂L/(∂q dot))δ(q dot) Why lowecase delta? What kind of notation is that? There is kind of a brief explanation at 00:23:00 but I don't really get it. If someone can show that a bit more clearly that would be helpful.