Common notations are prefix notation (+, -, not), postfix notation (factorial: n!), and functional notation (sin x or sin (x)). In the case of the square root a horizontal bar over the argument extending the square root sign can indicate the extent of the argument, so that parentheses can be dispensed with.
Unary operators (called "monadic" in APL) are also used in programming languages. For example, in the C family of languages, the following operators are unary:
- Increment: ++x, x++
- Decrement: --x, x--
- Address: &x
- Indirection: *x
- Positive: +x
- Negative: -x
- One's complement: ~x
- Logical negation: !x
- Sizeof: sizeof x
- Sizeof: sizeof(type-name)
- Cast: (type-name) cast-expression
While the above definition of a unary operation on a set S makes sense, the set must be specified. Without that, any arbitrary input can always be considered as a single entity of some, possibly quite complex, structure.