**Puzzle 171.** Yes, \$$\Phi(E,c) = \text{true}\$$ because we can first walk from \$$E\$$ to \$$N\$$ and then fly from \$$N\$$ to \$$c\$$. I hadn't noticed this when creating this puzzle! Like Matthew, I thought the answer was \$$\text{false}\$$.

**Puzzle 172.** Yes, \$$\Phi(E,e) = \text{true}\$$ because we can first walk from \$$E\$$ to \$$N\$$ and then fly from \$$N\$$ to \$$e\$$.

I should have given an example that was a bit different, like \$$\Phi(S,d)\$$.