I'm writing a academic paper and need to represent "A is not the empty set". What is usual way for professional mathematicians?
My idea is:
$|A| > 0$
However, using the emptyset $\emptyset$ might be more intuitive:
$A\ != \emptyset$
But, I know "!=" is not permissible in math community (only in programmers).
Sorry, I fixed the second equation: $|A|\ != \emptyset \rightarrow A\ != \emptyset$