Is bool boolval

[Wout4]

fixes #452

[Dimosts]

Why include BoolVal locally and not globally?

My comment has to do in general with the structure of the file and its imports. We import BoolVal locally 3 times, while I guess needing it 3 times is enough to do it globally.

At the same time, we include globally things we use only once (iterable, combinations, math) or dont even use (chain).

[Wout4]

it's to avoid a cyclical import..
Don't know what the best way to deal with that is.
Other than that we just always use global imports.

Good point on removing unused imports though