Function notation writes the value assigned by a function 
to an argument 
as 
. A declaration
 |
states that 
has domain 
and codomain 
. The notation 
specifies the assignment rule, while 
denotes the image
of a subset 
of the domain.
Function Notation
See also
Domain, Function, ImageExplore with Wolfram|Alpha
References
Halmos, P. R. Naive Set Theory. New York: Springer-Verlag, 1974.Cite this as:
Weisstein, Eric W. "Function Notation." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/FunctionNotation.html