Hello, can someone explain to me how this user did his contour integration ?
https://math.stackexchange.com/a/2372334/272494
If we want to integrate from on $[0,-iR]$, then this is the same as integrating on $[0,R] \cup \{Re^{i \theta} : \theta \in [0,\pi/2] \}$. But then I don't understand how he obtains his result.