A function that turns a real number into another real number can be represented like $f : \mathbb{R}\to \mathbb{R}$
What is the analogous way to represent a function that turns an unordered pair of elements of positive integers each in $\{1,...,n\}$ into a real number? I guess it would almost be something like $f : \{1,...,n\} \times \{1,...,n\} \to \mathbb{R}$ but is there a better notation that is more concise and that has the unorderedness?