I visited the Institute for Advanced Study again for the spring term of 1955. I was on leave from Chicago in the fall at Columbia where they were offering me a tenured associate professorship and- that's when I became engaged to Margaret. I had met her in the spring at the Institute for Advanced Study where she worked as the assistant to a lady archaeology professor, and when she came back from England in the fall we saw each other a great deal and we became engaged in November or so. And I decided I didn't want to go back to Chicago right away, I wanted to spend the spring at the Institute for Advanced Study, which I did. And that was when, as I described, when Einstein died and they took pictures of Margaret along with the institute and so on. Well, the Yang-Mills theory was very new at that time, in the spring of 1955. I was quite interested in it, but an incident occurred that impressed me very much with the situation in mathematics and the relation between mathematics and science. SS Chern was visiting Princeton then. He was a very famous mathematician working at Berkeley and he had been Frank Yang's teacher in China. They knew each other very, very well. They spent a lot of time together, their children played together, their wives saw each other and so on and so forth, during that spring in Princeton. Well, Frank spoke once or twice about the Yang-Mills theory, which was quite new. And SS Chern gave a series of lectures in the other building on mathematics, speaking on fibre bundles. And a number of physicists who were mathematically inclined attended the lectures on fibre bundles. But even at the end of that lecture series, and even after Frank had given a talk or two on the Yang-Mills theory, no one realised that these were the same, essentially the same thing; that the Yang-Mills theory was a special case of a fibre bundle, a non-trivial fibre bundle. And this despite the fact that Frank and Chern were so close together, they - I mean so close, such close friends and such close associates. They saw each other all the time, each one explained his ideas and neither of them realised that these ideas were essentially the same. It's amazing. But it's a consequence of the mood in mathematics at that time.