We often encounter related orthogonality relationship between vectors and functions. We saw several cases in Part I and will see other cases in Part III.
References
1. Dennery P, Krzywicki A (1996) Mathematics for physicists. Dover, New York
2. Stakgold I (1998) Green’s functions and boundary value problems, 2nd edn. Wiley, New York
430
10 Introductory Green’s Functions