Consider the digits from zero to nine. One of these digits has a property that the others do not. It has nothing to do with any arithmetic properties.

Which digit is it, and why?

(This is the sort of puzzle that could have multiple answers. I will accept any reasonable answer.)

Submit your answer to Gene Wirchenko <genew@telus.net>. Your answer should be in the form of a proof. That means to show how your answer must be correct. **The deadline is Wednesday, June 25, 2014 at noon Pacific Time.** I will post the answer shortly after.