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$\begingroup$

Is there a name for a set together with a unary operation?

If so, where can I learn more about them? Is there anything interesting about them? Are they simply a special case of groups? It simply occurred to me and Googling around has failed me.

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    It is called a function from the set to itself....2012-04-01
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    You might also be interested in [involutions](http://en.wikipedia.org/wiki/Involution_%28mathematics%29). They tend to appear in all sorts of algebraic situations. See also [here](http://en.wikipedia.org/wiki/Semigroup_with_involution).2012-04-01
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    From [Wikipedia/Outline of algebraic structures#Simple structures](http://en.wikipedia.org/wiki/Outline_of_algebraic_structures#Simple_structures): "Unary system: S and a single unary operation over S."2012-04-01
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    I think some people define discrete dynamical systems that way.2012-04-01

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