In the following image I am specifically referring to the step that produces the result Eq. (4.3). Is the notation off to the side $| \;\,\cdot \frac{1}{\psi(x)f(t)}$ in this step standard? (To anyone else who is initially confused like I was, it just means to perform the operation after the vertical bar on the equation before the vertical bar.) If this notation is not standard, what would be the most standard way of conveying this?
