Mathematical correctness of terms

[altavir]

As mentioned by @dievsky, the current names of Algebras are not quite consistent with mathematical definitions. For example, NDField is not actually a field since not all elements are invertable (a structure with a single zero is not). This fact should be shown in the documentation. There could be also limited renaming in class names if there are clear candidates.

[CommanderTvis]

Actually, there had been already some violations of structures' properties: e.g., + in MstRing is not commutative.

[altavir]

Indeed, those things should be mentioned in documentation as well.

[CommanderTvis]

1. I made a mistake when called XOperations semiX in the doc comments.
2. I still propose introducing a separate class for Group.

[altavir]

I do not want to complicate APIuselessly, so some use-cases are in order. Could you create a separate use case issue for them?

[CommanderTvis]

Boolean algebra gives a ring where a + b = (a /\ -b) \/ (-x /\ y) and a * b = a /\ b

[CommanderTvis]

And multiplying boolean by scalar makes no sense of course.

[altavir]

As I already said, boolean algebra should be derived directly from Algebra and not inherit any intermediate steps.