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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def has_stack(self, s):
 """Tests whether store `s` is a stack, that is, it never moves from position 0."""

        for t in self.transitions:
            if t.lhs[s].position != 0:
                return False
            if t.rhs[s].position != 0:
                return False
        return True