import Subst ( mkTopTyVarSubst, substClasses )
import VarSet ( mkVarSet, varSetElems )
import TysWiredIn ( isFFIArgumentTy, isFFIResultTy )
-import Unique ( cCallableClassKey, cReturnableClassKey, hasKey )
+import PrelNames ( cCallableClassKey, cReturnableClassKey, hasKey )
import Outputable
\end{code}