One week ago, I asked a question on math.stackexchange.com (http://math.stackexchange.com/questions/209120/a-question-on-intuitionistc-propositional-logic). But nobody answered my question. So I present it here:

In the Kripke's semantics of intuitionistic propositional logic, the frames are all partially ordered frames. Prove that:

Two finite-rooted frames are isomorphic iff they validate the same formulas in the language of intuitionistic propositional logic.

Thanks very much.