code: def visit_BitVecSub(self, expression, *operands):
          
          left = expression.operands[0]
          right = expression.operands[1]
          if isinstance(left, BitVecAdd):
              if self._same_constant(left.operands[0], right):
                  return left.operands[1]
              elif self._same_constant(left.operands[1], right):
                  return left.operands[0]
docs: a - 0 ==> 0
              (a + b) - b  ==> a
              (b + a) - b  ==> a