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  "body": "\n## Definition\n\nLet $A$ be a set.\nA *unary operation* on $A$ is a [[finitary operation|EJ8YJVM9BW]] of arity $1$, that is, a [[function|0EPAT51DXQ]] $f \\colon A \\to A$.\n\n## Remarks\n\nExample: the absolute value $x \\mapsto \\abs{x}$ is a unary operation on $\\R$, because $\\abs{x} \\in \\R$ for every $x \\in \\R$.\n\nNon-example: the map $x \\mapsto 1/x$ is not a unary operation on $\\R$, because it is not defined at $0$.\nIt is a unary operation on $\\R \\setminus \\set{0}$.\n\nA unary operation is often written in prefix notation $f(x)$ or $-x$, in postfix notation $x^{-1}$ or $x!$, or with a bar $\\bar{x}$.\nHere $A^1$ is identified with $A$.\n",
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