empty set

A player who cannot move because the choice is from the empty set has lost.

You walked into the theater to a rather empty, moody set.

The empty set is an identity element for the operation of union.

Here the maximum of the empty set is taken to be zero.

Thus, the empty set is abstract because it cannot act on other objects.

But in the end, he'd always had to go home to an empty echoing set of walls.

The only closed sets are the empty set and X.

Therefore, the empty set is the only partition of itself.

Although the empty set has no members, it can be a member of other sets.

In particular, the empty set and the whole space are closed.