Chandrasekhar and Ferrari [59] have also reduced the time independent perturbation equations
(using a different gauge) into a 5th order system which involves
only the spacetime perturbations with the fluid perturbations
being calculated via algebraic relations from the spacetime
perturbations. It was later proven by Ipser and Price [112,
169] that this system of ODEs can be reduced to the standard
equations in the Regge-Wheeler gauge. That this is possible is
apparent from equations (51
,
52
,
53
,
54
) and it is discussed in [5]