- Introspective software, where the bug depends on prior bugs, sequencing, or the introspection itself. If you object to this one, consider one of the previous bugs itself being temporally sensitive.

- Range-based bugs revealed by stochastic inputs, where those inputs necessarily arise from an external source (such as an atomic source).

- Any program whose state reflects or includes the environment, and that environment is mutable or consumable. Good luck testing your printer driver bug with no paper (or a software condition that only arises from incorrect handling of a hardware fault). Obviously, printers are a bit of an exaggerated case, but I’m sure you get my point. Simulated interfaces are all well and good, but might be insufficient.

In conclusion — I mostly agree with you. GP computers can emulate any other GP computer, so pure software can always have its execution environment perfectly replicated — *in theory*. Where practice is necessarily different, or the computer is not replicable (as in, say, some kind of "world computer"), then I disagree.

Of course