I am not very well versed on set theory or syntax, but I thought I knew the basics.
However, in a book about databases I am reading now, the author uses $2^x$ to signify "a set of $x$."
For example, $2^{\text{dogs}}$ is a set of $\text {dogs}$, etc.
The author never really explained this or why he does it, I just picked up the meaning from context.
I am not sure why the exponent operator is used, nor am I sure what the number $2$ has to do with it. The sets being represented are NOT powers of $2$ (in size)... they come in all sizes.
Is this a valid notation? I have not seen it anywhere before...