Conversation so far:
When did Richard Stallman go to Harvard University?
As a first-year student at Harvard University in fall 1970, Richard Stallman was known for his strong performance in Math 55.
What did Richard Stallman study at Harvard University?
Richard Stallman received a bachelor's degree in physics from Harvard in 1974.
When did Richard Stallman go to Massachusetts Institute of Technology?
Richard Stallman considered staying on at Harvard, but instead decided to enroll as a graduate student at the Massachusetts Institute of Technology.

Question: What did he study there?
Self-contained rewrite: What did Richard Stallman study at Massachusetts Institute of Technology?