Iterator

[benbrastmckie]

I released a version with an iterator for the default and exclusion semantics. It still needs some tuning since currently it doesn't find very many counterexamples, but the couterexamples are all non-isomorphic. The docs for these theories provide further details.

[mbuit82]

An idea that may be worth it: if default is to be an example for how to implement a semantics that's not as straightforward as imposition (and not as complex as bimodal or exclusion), then noting what portions of the code in semantic.py have to do with iteration may be helpful to people looking through. I looked through it and it looked at a glance that the last 1k lines are basically only relating to that; if that's true then might not be a bad idea to put a big header saying "you can ignore this for making your own semantics unless you want non-isomorphic iteration"

Though actually, as I'm writing this, how feasible would it be to move the non-isomorphism stuff to SemanticDefaults? Ideally it's something that's built into the model checker and not into a semantics, right?

[benbrastmckie]

I've still got some work to do on this but the plan is to refactor semantic.py, moving all the iteration stuff into iteration.py.