I want to write the following equations in dynare but I don´t know how.

Psi=Piss/Pi where Piss is the inflation rate in steady state and pi is the inflation rate. Obiously Psi in steady state should be 1. Note I don´t want to use Piss as a parameter, because if I change the parameters model I should get another steady state inflation.

As another example, how should I introduce the following process:

Log(R(t) / R)= taupi * log(pi(t)/pi) + tauy * log(y(t)/y)+ epsilonr(t)

where the variables without (t) are the variables in steady state. For example pi is pi(t) in steady state.

Thank you so much.