I'm sorry, but this post is utterly pedantic. The proof by Daniel Levine is absolutely "logically sound." The idea that what was shown was the conditional, "if

I'm sorry, but this post is utterly pedantic. The proof by Daniel Levine is absolutely "logically sound." The idea that what was shown was the conditional, "if y=y then x0=0" and not "x0=0 is true" simply ignores the fact that the first proposition in the proof was NOT an implication or derivation - it was an axiom. Because it is an axiom, we are guaranteed that the argument is sound (and the conclusion true under whatever interpretation allows proposition #1 as an axiom) as soon as we prove that the argument is valid. Which is exactly what Levine set out to show. Logic 101.