1. The problem statement, all variables and given/known data Now in a revision lecture given a few weeks ago, the lecturer gave this as the answer. 3. The attempt at a solution No I think generally I'm fine with it (apart from it doesn't seem very obvious that this is what you should do with the maths!). BUT 1) Where do the subscript m's come from? Why aren't they still n's like are used for the conjugate of [tex]\psi[/tex]? 2) How come the delta function suddendly gets rid of the sigma m, and itself, whilst simultaneously changing the am to an? And whats a good definition of orthogonality? A simple laymans definition!!