In mathematics, an argument of a function is a value that must be provided to obtain the function's result. It is also called an independent variable. For example, the binary function has two arguments, and , in an ordered pair . The hypergeometric function is an example of a four-argument function. The number of arguments that a function takes is called the arity of the function. A function that takes a single argument as input (such as ) is called a unary function. A function of two or more variables is considered to have a domain consisting of ordered pairs or tuples of argument values. The argument of a circular function is an angle. The argument of a hyperbolic function is a hyperbolic angle.