Suppose that, for the binary operation ○ on the set S, there is an identity element e. An element a′ is an inverse (or inverse element) of the element a if a○a′ = a′○a = e. If the operation is called multiplication, the identity element may be denoted by 1. Then the inverse a′ may be called a multiplicative inverse of a and be denoted by a⁻¹, so that aa⁻¹ = a⁻¹ a = 1 (or e). If the operation is addition, the identity element is denoted by 0, and the inverse a′ may be called an additive inverse (or a negative) of a and be denoted by −a, so that a + (−a) = (−a) + a = 0. See also group.