Read DeBurca. I am guessing you go to Swansea since this is one of the seminar questions for the week =P. I have not answered the question yet, but I know there is a detailed section in the required reading in DeBurca on Keck/before and after. Also if you attended the lecture, Keck was gone over in quite a lot of detail so just refer to your notes from that lecture to point you in the right direction.