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Section 2.2 Session 2

It feels kind of silly to post solutions to a problem set that includes the answers already, but this seems like a good opportunity to validate my generalization from last week.

Example 2.2.1. Problems on the number of maps from one set to another.

How many maps...
Solution.
We have answers here, so let’s confirm the results of the generalization from Article 1:
Table 2.2.2.
# \(||A||\) \(||B||\) Expression Result Correct
1 4 1 \(1^4\) 1 YES
2 1 4 \(4^1\) 4 YES
3 0 4 \(4^0\) 1 YES
4 4 0 \(0^4\) 0 YES
5 0 0 \(0^0\) "it depends" "mostly"
The generalization seems to hold up, provided we define our exponential operator in such a way that \(0^0=1\text{.}\) This is a common practice, but I’ve also seen situations where \(0^0\) is left undefined instead. In this context, the answer of 1 to problem 5 makes more sense than than the alternative. In programming terms, it seems perfectly reasonable to think of "no op" as a "function" so there should be an analogous "null map" that maps from nothing to nothing.