“PA is not expressible as a first-order statement.” Countable sets of first-order statements still count. But, yes, this is getting rather far off-topic.
http://en.wikipedia.org/wiki/G%C3%B6del%27s_completeness_theorem
“PA is not expressible as a first-order statement.” Countable sets of first-order statements still count. But, yes, this is getting rather far off-topic.
http://en.wikipedia.org/wiki/G%C3%B6del%27s_completeness_theorem