A term such as ‘Sine 60°’, or ‘the father of Hegel’ refers to a number or a person. But it includes the term ‘Sine…’ or ‘father of…’. ‘Sine x’ or ‘father of y’ stand for a function referring respectively to a number or a person for particular values of x and y. If we wish to refer to the function itself, the notation (λx)(Sine x) or (λy) (father of y) is adopted. A logical calculus with rules involving such terms is called the lambda calculus.