Rename Polynomial

[geisserf]

Issue imported from old repository.

Polynomial is also used for logic expressions. We should think of a better Class name.

I think we agreed in the discussion in the old repository to rename Polynomial to Expression, but reading it now we already have an Expression class.

[digitalw]

In my thesis I talk about functions over monoids. We could simply use Function or MonoidFunction.

[geisserf]

But with function I more likely associate the operators between two evmdds (or monoid elements), such as = and -. Additionally an evmdd in itself is a function from states to monoid elements, so I think this would overload the term even more.

We could also think of renaming the current expression class and use the term expression for what is currently a polynomial.

[digitalw]

We could rename Expression to Operators as it is exactly that. Later on this class would simply aggregate the existing operators anyway (See Issue #6 )

[geisserf]

Well, it's not completely only operators, as the Expression also contains variables and numbers. If we think of an expression as an abstract syntax tree, then the current Expression class consists of all possible nodes of that tree (i.e. operators, variables and numbers).

[digitalw]

How about something along AstNode then