# Is (2,3),(-4,5),(-2,7),(7,7) a function?

If we define a function $f : \left\{- 4 , - 2 , 2 , 7\right\} \to \left\{3 , 5 , 7\right\}$, such that $f \left(- 4\right) = 5 , f \left(- 2\right) = 7 , f \left(2\right) = 3 , f \left(7\right) = 7$ then $f$ is indeed a function.
We note that $f$ is surjective in this case but not injective. Also, we could pick any number set to be the codomain of $f$, but this would make $f$ non-surjective.