The function from a given nonempty set 
to the power set 
that maps every element 
of 
to the set 
.
Singleton Function
See also
Nonempty Set, Power SetThis entry contributed by Margherita Barile
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Cite this as:
Weisstein, Eric W., with contributions by Margherita Barile. "Singleton Function." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/SingletonFunction.html