Does anyone know how to derive the Ward-Takahashi identity for a field starting from a known conserved Noether current (or equally helpful, from a known symmetry transformation of the Lagrangian)? It'll probably be enough to allow me to do it for myself if you could explain quantitatively what the Ward-Takahashi identity is. Please don't quote wikipedia to me, from a pedagogical standpoint it has all the teaching prowess of an amoeba.