'Removes particle/fills hole in orbit i. No input tests performed here.'

def _remove_orbit(self, i):

    new_occs = list(self.args[0])
    pos = new_occs.index(i)
    del new_occs[pos]
    if (pos % 2):
        return (S.NegativeOne * self.__class__(new_occs, self.fermi_level))
    else:
        return self.__class__(new_occs, self.fermi_level)
