$n$-ary operation, on a set $A$
$$\omega\colon A^n\to A$$
of the $n$-th Cartesian power of the set $A$ into the set $A$ itself. The number $n$ is known as the arity of the algebraic operation. Historically, the concepts of binary $(n=2)$ and unary ($n=1$) operations were the first to be considered. Nullary $(n=0)$ operations are fixed elements of the set $A$; they are also known as distinguished elements or constants. In the 20th century the concept of an infinitary operation appeared, i.e. a mapping $\omega\colon A^\alpha\to A$, where $\alpha$ is an arbitrary cardinal number. A set with a system of algebraic operations defined on it is called a universal algebra.
|[a1]||J. Stominski, "The theory of abstract algebras with infinitary operations" Rozprawy Mat. , 18 (1959)|
|[a2]||P.M. Cohn, "Universal algebra" , Reidel (1981) pp. 13–14|
Unary operation. Encyclopedia of Mathematics. URL: http://www.encyclopediaofmath.org/index.php?title=Unary_operation&oldid=39744