A bijection "f" with domain "X" (indicated by "f": "X → Y" in functional notation) also defines a converse relation starting in "Y" and going to "X" (by turning the arrows around). The process of "turning the arrows around" for an arbitrary function does not, "in general", yield a function, but properties (3) and (4) of a bijection say that this inverse relation is a function with domain "Y". Moreover, properties (1) and (2) then say that this inverse "function" is a surjection and an injection, that is, the inverse function exists and is also a bijection. Functions that have inverse functions are said to be invertible. A function is invertible if and only if it is a bijection.