Exponential notation for function spaces

https://arbital.com/p/5k7

by Izaak Meckler Jul 24 2016 updated Jul 25 2016

Why $Y^X$ is good notation for the space of maps from $X$ to $Y$


If $~$X$~$ and $~$Y$~$ are sets, the set of functions from $~$X$~$ to $~$Y$~$ (often written $~$X \to Y$~$) is sometimes also written $~$Y^X$~$. This latter notation, which we'll call exponential notation, is related to the notation for finite powers of sets (e.g., $~$Y^3$~$ for the set of triples of elements of $~$Y$~$) as well as the notation of exponentiation for numbers.

Without further ado, here are some reasons this is good notation.

More generally, $~$Y^X$~$ is good notation for the exponential object representing $~$\text{Hom}_{\mathcal{C}}(X, Y)$~$ in an arbitrary cartesian closed category $~$\mathcal{C}$~$ for the first set of reasons listed above.


Comments

Patrick Stevens

If $~$X$~$ and $~$Y$~$ are sets, the set of functions from $~$X$~$ to $~$Y$~$ \(often written $~$X \\to Y$~$\) is sometimes also written $~$Y^X$~$\. This latter notation, which I'll call exponential notation, is related to the notation for finite powers of sets \(e\.g\., $~$Y^2$~$ for the powers of triples of elements of $~$Y$~$\) as well as the notation of exponentiation for numbers\.

I don't think this is what you mean, is it?

Izaak Meckler

Thanks, I've corrected it. That was a strange typo.