+We need to both 'unBox' and zonk deferred types. We need to unBox as
+functions, such as TcExpr.tcMonoExpr promise to fill boxes in the expected
+type. We need to zonk as the types go into the kind of the coercion variable
+`cotv' and those are not zonked in Inst.zonkInst. (Maybe it would be better
+to zonk in zonInst instead. Would that be sufficient?)
+