--- a/lib/ur/top.ur	Thu Mar 10 20:22:03 2011 -0500
+++ b/lib/ur/top.ur	Fri Mar 11 18:36:24 2011 -0500
@@ -61,13 +61,15 @@
 
 con mapU = K ==> fn f :: K => map (fn _ :: Unit => f)
 
-con ex = fn tf :: (Type -> Type) =>
-            res ::: Type -> (choice :: Type -> tf choice -> res) -> res
+con ex = K ==> fn tf :: (K -> Type) =>
+            res ::: Type -> (choice :: K -> tf choice -> res) -> res
 
-fun ex [tf :: (Type -> Type)] [choice :: Type] (body : tf choice) : ex tf =
- fn [res] (f : choice :: Type -> tf choice -> res) =>
+fun ex_intro [K] [tf :: K -> Type] [choice :: K] (body : tf choice) : ex tf =
+ fn [res] (f : choice :: K -> tf choice -> res) =>
     f [choice] body
 
+fun ex_elim [K] [tf ::: K -> Type] (v : ex tf) [res ::: Type] = @@v [res]
+
 fun compose [t1 ::: Type] [t2 ::: Type] [t3 ::: Type]
             (f1 : t2 -> t3) (f2 : t1 -> t2) (x : t1) = f1 (f2 x)