1 files changed, 9 insertions, 0 deletions
diff --git a/Test/dafny2/COST-verif-comp-2011-2-MaxTree-class.dfy b/Test/dafny2/COST-verif-comp-2011-2-MaxTree-class.dfy
index c752bd38..f691384c 100644
--- a/Test/dafny2/COST-verif-comp-2011-2-MaxTree-class.dfy
+++ b/Test/dafny2/COST-verif-comp-2011-2-MaxTree-class.dfy
@@ -117,6 +117,11 @@ class Tree {
     Repr := lft.Repr + {this} + rgt.Repr;
   }
 
+  lemma exists_intro<T>(P: T -> bool, x: T)
+    requires P.requires(x)
+    requires P(x)
+    ensures exists y :: P.requires(y) && P(y) { }
+
   method ComputeMax() returns (mx: int)
     requires Valid() && !IsEmpty();
     ensures forall x :: x in Contents ==> x <= mx;
@@ -124,13 +129,17 @@ class Tree {
     decreases Repr;
   {
     mx := value;
+
     if (!left.IsEmpty()) {
       var m := left.ComputeMax();
       mx := if mx < m  then m else mx;
     }
+
     if (!right.IsEmpty()) {
       var m := right.ComputeMax();
       mx := if mx < m then m else mx;
     }
+
+    exists_intro(x reads this => x in Contents && x == mx, mx);
   }
 }