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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 follow_char(self, label, index):
        "Follows a transition"
        offset = units.offset(self._units[index])
        next_index = (index ^ offset ^ label) & units.PRECISION_MASK

        if units.label(self._units[next_index]) != label:
            return None

        return next_index