+ --
+ -- We use tcInstSkolType because we don't want to allocate fresh
+ -- *meta* type variables.
+ --
+ -- We use UnkSkol --- and *not* InstSkol or PatSkol --- because
+ -- these variables must be bindable by tcUnifyTys. See
+ -- the call to tcUnifyTys in InstEnv, and the special
+ -- treatment that instanceBindFun gives to isOverlappableTyVar
+ -- This is absurdly delicate.
+