static Evaluation Sw(const Params& params, const FluidState& fs)
 {
     const Evaluation& pC =
         Opm::decay<Evaluation>(fs.pressure(Traits::nonWettingPhaseIdx))
         - Opm::decay<Evaluation>(fs.pressure(Traits::wettingPhaseIdx));
     return twoPhaseSatSw(params, pC);
 }
    static Evaluation Sw(const Params &params, const FluidState &fs)
    {
        typedef MathToolbox<typename FluidState::Scalar> FsToolbox;

        Evaluation pC =
            FsToolbox::template toLhs<Evaluation>(fs.pressure(Traits::nonWettingPhaseIdx))
            - FsToolbox::template toLhs<Evaluation>(fs.pressure(Traits::wettingPhaseIdx));
        return twoPhaseSatSw(params, pC);
    }
 static Evaluation twoPhaseSatSn(const Params& params, const Evaluation& pc)
 { return 1 - twoPhaseSatSw(params, pc); }