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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 _latex_(self):
 r"""The representation routine for transitions. '^{133}\\mathrm{Cs}\\ 6S_{1/2}^{4}\\ \\nrightarrow \\ ^{133}\\mathrm{Cs}\\ 6S_{1/2}^{3}' """

        if self.allowed:
            return self.e1._latex_()+'\\ \\rightarrow \\ '+self.e2._latex_()
        elif not self.allowed:
            return self.e1._latex_()+'\\ \\nrightarrow \\ '+self.e2._latex_()
        else:
            return self.e1._latex_()+'\\ \\rightarrow^? \\ '+self.e2._latex_()

        return self.e1._latex_()+'\\ \\nleftrightarrow \\ '+self.e2._latex_()