[Gretl-users] Fama and French using GMM in Grelt

Dear All,              I have a qualm applying a four-factor Fama and French model with Grelt. The reference article I''m using applies GMM. As far as I have perused GMM goes with instruments(moment conditions). But in this article, no reference is made to choice of instruments. Is there a GMM application on Grelt that doesn't require instruments for its application?.              Cheers ________________________________