The **tombstone**, **halmos**, or end of proof mark "∎" is used in mathematics to denote the end of a proof, in place of the traditional abbreviation "QED" for the Latin phrase "quod erat demonstrandum" (Q.E.D.)- which literally means "which was to be demonstrated"

It is sometimes called a halmos after its eponym Paul Halmos, who first used it in mathematical context, after seeing it was being used to indicate the end of articles in magazines.

I dug a little deeper and found that Halmos obtained his B.A. from the **University of Illinois**! He majored in philosophy and minored in mathematics and graduated in three years at 19.