Incorrect results for less than or equal and greater than or equal

[Kasche153]

Seems to be an error for >= and <= operators when compared to ==.

Example:

 >>>comparator = Comparator()
 >>>print(comparator.compare("x <= y", "x == y"))
 >>>The predicates are not equivalent and neither is stronger.
 >>print(comparator.compare("x >= y", "x == y"))