Talk:2.9.4/@comment-5149782-20120616222858

This first suggested solution is incorrect (as I showed by an example), but the first part of the solution looks okay (I didn't realize that until I had written an almost identical answer ...).

However, maybe it's a matter of interpretation. I would say that the sum of the digits of e.g. $$-11$$ is $$1 + 1 = 2$$, but I guess one could claim that one should use the sum $$-(1 + 1) = -2$$ as the first answer does (which would make the proposition true because of the $$-x \equiv -y \pmod{9} \iff x \equiv y \pmod{9}$$ thing).

Edit: okay, I changed my mind, maybe it's better to call it an "alternative solution".