Hello, my question is a simple one: I am attempting to do problem 2.31 in Griffiths' QM book (latest edition). The question states, "The Dirac Delta function can be thought of as the limiting case of a rectangle of area 1, as the height goes to infinity and the width to zero. Show that the Delta-function well is a "weak" potential, in the sense that z0 -> 0. ..." What is z0 in this case? I've not seen it introduced anywhere in the book and there's no description for what it represents. I'm not sure if I'm missing something obvious but any help would be great.