new apply almost there

[helm.git] / helm / software / matita / library / didactic / exercises / natural_deduction_fst_order.ma

diff --git a/helm/software/matita/library/didactic/exercises/natural_deduction_fst_order.ma b/helm/software/matita/library/didactic/exercises/natural_deduction_fst_order.ma
index 9a865597b02879bc45ddc827827155693faef0ee..dfecc3c1346325d67ab4aca0a92d5572953d58b0 100644 (file)
--- a/helm/software/matita/library/didactic/exercises/natural_deduction_fst_order.ma
+++ b/helm/software/matita/library/didactic/exercises/natural_deduction_fst_order.ma
@@ -193,7 +193,7 @@ apply rule (prove (¬(∀x.P x) ⇒ ∃x.¬ P x));
 apply rule (⇒_i [h1] (∃x.¬ P x));
 apply rule (RAA [h2] (⊥));
 apply rule (¬_e (¬(∀x.P x)) (∀x.P x));
-       [ apply rule (discharge [h1]);
+       [ apply rule (discharge [h2]);
        | apply rule (∀_i {y} (P y));
     apply rule (RAA [h3] (⊥));
     apply rule (¬_e (¬∃x.¬ P x) (∃x.¬ P x));