unfold forces_t in |- *; unfold forces_t2 in |- *; simpl in |- *.
intros; elimtype False; assumption.
Qed.

Lemma forces_a_imp_b_imp_c__forces_a_imp_falsum_imp_c :
forall (k : kripke_tree) (a b c : form),
forces_t k (Imp (Imp a b) c) -> forces_t k (Imp (Imp a Falsum) c).