How would one denote the set of all subsets of $A$ which have size $2$?
Would $\binom{A}{2}$
be a good idea?
How would one denote the set of all subsets of $A$ which have size $2$?
Would $\binom{A}{2}$
be a good idea?
$\dbinom A 2$ is standard notation for the set of all size-$2$ subsets of a set $A$, in the usage of combinatorialists.
In set theory it can be often denoted as $[A]^2=\{\{a,b\}:a,b\in A, a\neq b\}$.