Empty function
In mathematics, an empty function is a function whose domain is the empty set ∅. For each set A, there is exactly one such empty function
The graph of an empty function is a subset of the Cartesian product ∅ × A. Since the product is empty the only such subset is the empty set ∅. The empty subset is a valid graph since for every x in the domain ∅ there is a unique y in the codomain A such that (x, y) ∈ ∅ × A. This statement is an example of a vacuous truth since "there is no x in the domain."