Thank you for finding it. I was interested in seeing how difficult the problems were. The first page does seem it requires knowledge of calculus and partial der

Thank you for finding it. I was interested in seeing how difficult the problems were. The first page does seem it requires knowledge of calculus and partial derivatives. The problems he referred to are of the "Examples for Solution" kind like the one on page 3. For motivation, Dyson also said "The difference between a text without problems and a text with problems is like the difference between learning to read a language and learning to speak it. I intended to speak the language of Einstein, and so I worked my way through the problems. I started at six in the morning and stopped at ten in the evening, with short breaks for meals. I averaged fourteen hours a day. Never have a I enjoyed a vacation more."