  An important class of these identity statements are statements of the form ‘\(f(x) = y\)’, where \(f(\:)\) is any unary function (i.e., function of a single variable), \(x\) is the argument of the function, and \(f(x)\) is the value of the function for the argument \(x\). Similarly, \(f(x,y) = z\) is an identity statement involving a binary function of two variables. And so on, for functions of more than two variables.