@user21820 I am not sure that I can see a good reason to close C9 (though I'm willing to be convinced). It seems to have context ("my book says no direct generalization is possible..."), and outlines what kind of counterexample they are looking for. As the question is several years old, I'm not sure that I can justify the use of a close vote on it.
@user21820 C3 ought to be Roomba'd in the next day or two (FYI).