Find a common domain for the variables x,y, and z for which the statement ∀x∀y((x≠y)→∀z((z=x)∨(z=y))) is true and another domain for which it is false.
This problem stumped me. I wrote:
The statement is true for any binary domain (such as {0,1}) and false for any non binary domain.
The corrected paper stated that "non binary domain" was incorrect. I am guessing that this is simply a matter of sloppy wording and that "greater than binary" would be correct.
It also stated that I needed to justify my answer. Can anyone give me a starting point for how I would approach a proof?