  The inverse method is a saturation based theorem proving technique; it relies
on a forward proof-search strategy and can be applied to cut-free calculi
enjoying the subformula property. Here we apply this method to derive the
unprovability of a goal formula G in Intuitionistic Propositional Logic. To
this aim we design a forward calculus FRJ(G) for Intuitionistic unprovability
which is prone to constructively ascertain the unprovability of a formula G by
providing a concise countermodel for it; in particular we prove that the
generated countermodels have minimal height. Moreover, we clarify the role of
the saturated database obtained as result of a failed proof-search in FRJ(G) by
showing how to extract from such a database a derivation witnessing the
Intuitionistic validity of the goal.
