Definition:Halmos Symbol

Definition
The Halmos symbol is the character: used to indicate the end of a proof.

It replaces the old-fashioned and embarrassingly uncool Q.E.D. which muggles sometimes use when pretending to be clever.

Also defined as
Some sources show this, in some contexts, as a heavy vertical line, something like: $\Rule{3px} {2ex} {0ex}$ rather than a box, but the intention is the same.

This form is used, for example, by in his  to indicate the point of termination of an algorithm.

It was he who was credited with introducing it into mathematics, having seen it used in general magazine literature to indicate the end of an article:


 * The symbol is definitely not my invention — it appeared in popular magazines (not mathematical ones) before I adopted it, but, once again, I seem to have introduced it into mathematics. It is the symbol that sometimes looks like $\Box$, and is used to indicate an end, usually the end of a proof. It is most frequently called the 'tombstone', but at least one generous author referred to it as the 'halmos'.