 The set is called the "domain" of the operation, the set "Y" is called the "codomain" of the operation, and the fixed non-negative integer "n" (the number of operands) is called the "arity" of the operation.Thus a unary operation has arity one, and a binary operation has arity two.An operation of arity zero, called a "nullary" operation, is simply an element of the codomain "Y".