“Basically it’s just a matter of thinking. Often you write something down to clarify your thoughts, but not necessarily. In particular, when you’ve reached a real impasse, when there’s a real problem that you want to overcome, then the routine kind of mathematical thinking is of no use to you. Leading up to that kind of new idea there has to be a long period of tremedous focus on the problem without any distraction. You have to really think about nothing but that problem–just concentrate on it. Then you stop. Afterward there seems to be kind of a period of relaxation during which the subconscious appears to take over, and it’s during that time that some new insight comes.”