These exercises are meant to be suggestions for the students of the QFT1 lectures.
They are a preparation for the final exercises and a way to extend some of the
concepts presented in the lectures.
Unfortunately, there won't be time to solve them in the class. Moreover, I have
not a clean version of the solutions yet. However, I will be happy to provide hints
and discussions in my office and in the lecture breaks, if students desire.

Please note that sign and normalization conventions are not uniform in QFT. Almost 
every author has her/his own ones and sometimes typos are even present. In the lecture, 
I try to be as consistent as possible with Peskin, Schoreder conventions. Nevertheless,
it is very likely that there will be sign mistakes in the lectures as well as in the
exercises. So, don't mind if there is a (global) - sign in your solutions.