[Gretl-users] Restriction on model coefficients

Hello everyone, I need to estimate an equation with tsls. This equation has a restriction on parameters. The restriction has inside itself values coming from the estimation parameters of another equation and it is the following: b3=[a1/(1-a2)](1-b2)-b1, on which "a" indicate a parameter of the first equation (already estimated) and "b" indicate a parameter of the second equation (which has to be estimated with tsls) and the numbers indicate the parameter associated to a regressor. How can I estimated the second equation once I have estimated the first. Thank you for the support!