Assume that $L$ is a language, is there any established notation that means that $L$ is infinite or empty?
The usual way to describe these properties is by indicating the size of $L$, denoted by $|L|$.
- Empty language, the size is zero, $|L|=0$
- Finite language, $|L|=c$ or in general, the size in non-infinite, $|L|< \infty$
- Infinite language, $|L|=\infty$.