[schoen]

You could be a little more precise and say that it's NP-complete. :-)

[OxO4]

That actually depends on the logic being used. Some of the logics supported by Z3 are not even decidable. In fact, even solving quantifier-free bit-vector formulas is NEXPTIME-complete [0] when using a binary encoding.

[0] http://smt2012.loria.fr/paper7.pdf

[schoen]

Thanks for the clarification!

What do Z3 and other SMT solvers do if you ask them about undecidable questions? Do they potentially run forever?