I was so lucky to have, as a teacher- this was in high school- in algebra, Lida F Baldwin. She was a soul of integrity and she told us all to put things together in a clear, clean, honest way. I was interested to learn that my later colleague, Marvin Goldburger, who became, subsequently, the President of the California Institute of Technology, went to the same high school in Youngstown that I did, and had her also as his teacher. And then a Miss Doerschuk, another mathematics teacher, had a wonderful scheme of giving out little pieces of paper, like dealing cards off a deck of cards, to we students, and there, on each piece of paper, was written something to be proved. For example, that the bisector of an angle does this or that to the opposite side of the triangle. And she called on the students in turn to go walk up to the board, state the theorem and then provide the proof, which generally was extemporaneous, because one didn't have time to think about it very much in detail. This is marvellous training for anybody giving a course when he doesn't have time to get ready for the course in advance.