Well, Kemmer gave two courses which were both excellent. One was nuclear physics and one was quantum field theory, and quantum field theory was at that time very much of a continental subject. It hadn't been done much in England, even less in America. It was essentially a German monopoly almost. I mean, it was invented by Heisenberg and Pauli and a few other people, Wigner, and it had all been developed more or less in Germany and Switzerland, and the classic book on the subject was Wentzel, Zur Quantentheorie der Wellenfelder, which was published in Vienna in the middle of the war and was completely inaccessible to anybody in England or America. So Kemmer had brought this book with him, or had a copy of it in Cambridge, and so he gave me that to read. And that was, of course, a tremendous advantage because that contained quantum field theory set out very clearly in a very orderly fashion, explaining just what was known and what was not known, and that was the tool that I needed, actually, for quantum electrodynamics. It had not been put together. There was Heitler's book which was very phenomenological, describing the calculations that had been done; and Wentzel's book which gave you the general mathematical framework very nicely, but the two had never really been combined. Anyhow, so I had those two things very fortuitously put together, and that was exactly the right preparation then for what I did in America.