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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 iter_sys(self):
 """ Iterate over sys_name, overall_sys, histo_sys. overall_sys or histo_sys may be None for any given sys_name. """

        names = self.sys_names()
        for name in names:
            osys = self.GetOverallSys(name)
            hsys = self.GetHistoSys(name)
            yield name, osys, hsys