Truth value of an expression (Boolean Polynomials)

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@tmonteil Thanks. In my current situation, I get the truth values of the variables from solving a SAT problem. Thus, I have a dictionary like `{s0: True, s1: False}`, I need that these values are put to the expression. But I am stuck with that! Can you help me?

@tmonteil But, more than 256 variables is not allowed in this method!

@tmonteil Moreover, I found that instead of doing calculations over finite of degree 2, it simply calculates the value!!

Well, this how a boolean expression should be called, see `expr.__call__?` for more details. Now, if you want to evaluate according to a dictionary, you can type `expr.substitute(d)` or `bool(expr.substitute(d))`. I didn't check, but if you need more than 256 variables and it does not work, you should open a ticket on the trac server http://trac.sagemath.org . Concerning the values, this is the way Python handles boolean: 0 stands for `False` and any positive int stands for `True`, you can notice that it is consistent with the addition as the or `and` the multiplication as the `and`. By the way, to see all available methods that can be applied to `expr`, you can type `expr.[TABULATION]` and see the list.

Another problem, how can I use something like: (expr([s'%d'%(i)=True for i in range(2)])) ?