Factoring is in a category. Everything computable exists somewhere. We know factoring to be in NP.

What I was disagreeing with was the “at least” and “at most” characterization of NP completeness. It is a set, not a boundary. The actual diagram of the complexity zoo is much more complicated than concentric circles.

And for verifiability, I was not referring to it as an existential sort of thing. I was simply saying that I agreed with you in that particular facet, but it isn’t sufficient to describe NP completeness. You also need NP-hardness.