'Returns a NO() without FermionicOperator at index i.
Examples
>>> from sympy import symbols
>>> from sympy.physics.secondquant import F, NO
>>> p,q,r = symbols(\'p,q,r\')
>>> NO(F(p)*F(q)*F(r)).get_subNO(1)  # doctest: +SKIP
NO(AnnihilateFermion(p)*AnnihilateFermion(r))'

def get_subNO(self, i):

    arg0 = self.args[0]
    mul = arg0._new_rawargs((arg0.args[:i] + arg0.args[(i + 1):]))
    return NO(mul)
