(At least) ExactSumConstraint doesn't handle negative numbers properly #33
Description
myth1 python-constraint-master # python
Python 2.7.12 (default, Dec 17 2016, 17:32:09)
[GCC 4.9.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> from constraint import *
>>> p = Problem()
>>> p.addVariable('a', [-1,0,1])
>>> p.addVariable('b', [-1,0,1])
>>> p.addConstraint(ExactSumConstraint(0), ['a', 'b'])
>>> print p.getSolutions()
[{'a': 0, 'b': 0}]
>>>
Shouldn't a==-1, b==1 and a==1, b==-1 also be solutions?
Thanks.