Mr. Zuckerberg declined to be interviewed, saying through a spokeswoman that he was not sure how to respond. He did not dispute the chronology of events or the authenticity of Mr. Greenspan’s e-mail messages. Mr. Zuckerberg is seeking to dismiss the ConnectU suit.

Mr. Greenspan said that Mr. Zuckerberg’s lawyer contacted him this year in connection with the ConnectU lawsuit but that he had declined a request to serve as a witness, fearing that he would become embroiled in the legal battle.

In an interview at a cafe here this week, Mr. Greenspan said he had mostly made peace with the fact that Mr. Zuckerberg will be the first of his classmates to become a billionaire.

If Mr. Zuckerberg did borrow some of Mr. Greenspan’s concepts, he may have simply been working in a grand Harvard tradition. After all, it was a young Harvard dropout, Bill Gates, and his classmate, Paul G. Allen, who almost three decades earlier copied a version of the BASIC programming language, designed by two Dartmouth college professors, to jump-start the company that would grow into the world’s most powerful software firm.

“I’ve had a long time to think about this, and I’m not as bitter as I was a year ago,” Mr. Greenspan said. “Things like this aren’t surprising to me anymore.”

Still, he does not seem to be entirely at peace with the way things have turned out, and he wants to have the last word.

Image Mark E. Zuckerberg, the chief executive of Facebook. Credit... Noah Berger for The New York Times

He has described the original creation of houseSYSTEM, ConnectU and Facebook in “Authoritas: One Student’s Harvard Admissions,” a 306-page unpublished autobiography about his adventures as a college student.