A set/category theoretic interpretation.
Encoding 0 and 1 as sets
The standard encoding of the natural numbers as sets gives:
- 0 is the empty set $${}$$.
- 1 is a set that contains 0. In set notation, it's $${0}$$. Unfolding the definition further, it's a set that contains the empty set, $${{}}$$.
Counting functions with exponents
Target^Source can be interpreted as the set of all functions from Source to
Target. This is seen in the powerset notation $$2^X$$, where we can identify
subsets of $$X$$ with maps into a 2 element set, where 1 element indicates "yes
this is in the subset" and the other indicates no.
Examples
Let
- Source := $${1, 2}$$
- Target := $${3}$$
There is exactly 1 function between these sets, which sends both 1 and 2 to 3. The exponential formula predicts $$1^2 = 1$$ possible functions, which checks out.
Let
- Source := $${}$$
- Target := $${1}$$
There is exactly 1 function between them, the empty set.
The empty set can be interpreted as a function because functions are subsets of
the Cartesian product Source x Target. An empty set meets this criteria.
Let
- Source := $${1}$$
- Target := $${}$$
There are no functions between them because all elements of Source must be mapped to something, but there's nothing to map to. The exponential formula gives $$0^1 = 0$$ total functions.
Finally, let
- Source := $${}$$
- Target := $${}$$
There's nothing in Target to map to, but there's also nothing that needs mapping from since Source is empty too. So the empty set is a valid function between them.
Therefore, the set of all functions between empty sets (aka 0) is a set that contains the empty set. Which is 1, by the standard encoding given above.
A nice confluence.