class-method-types.md

@@ -34,7 +34,7 @@ data SomeFoo = exists a . Foo a => SomeFoo a
 ```
 
 
-would have to carry around a dictionary for Num as well as Foo in dictionary passing implementation of type classes.
+would have to carry around a dictionary for Num as well as Foo in dictionary passing implementation of type classes. In general some sort of fixpoint iteration would be needed to determine the set of dictionaries needed on an existential type.
 
 
 ## Cons