I suspect an error in the solution given to a logic problem in the book To Mock a Mockingbird (Chapter 3 Problem 2).
Suppose I told you that the town contains two barbers, Arturo and Roberto, and that Arturo shaves all and only those inhabitants who shave Roberto, and Roberto shaves all and only those inhabitants who don't shave Arturo. Does this lead to a paradox?
No, this is no paradox. It could be that Roberto shaves himself, Arturo shaves Roberto, Arturo doesn't shave himself, and Roberto doesn't shave Arturo. The other X's in the town don't really matter; indeed, Arturo and Roberto could just as well be the town's only inhabitants.
The problem I have with this answer is that "Arturo doesn't shave himself" and "Roberto doesn't shave Arturo" while the problem states that "Roberto shaves all and only those inhabitants who don't shave Arturo". Therefore shouldn't Roberto also shave Arturo (invalidating the answer)? Or am I missing something?