+init_in_scope :: InScopeSet
+init_in_scope = mkInScopeSet (unitVarSet (mkWildValBinder unitTy))
+ -- See Note [WildCard binders]
+\end{code}
+
+Note [WildCard binders]
+~~~~~~~~~~~~~~~~~~~~~~~
+The program to be simplified may have wild binders
+ case e of wild { p -> ... }
+We want to *rename* them away, so that there are no
+occurrences of 'wild' (with wildCardKey). The easy
+way to do that is to start of with a representative
+Id in the in-scope set
+
+There should be no *occurrences* of wild.
+
+\begin{code}