| CoTyApps [Type] -- [] t1 .. tn
| CoLams [Id] -- \x1..xn. []; the xi are dicts or coercions
| CoTyLams [TyVar] -- \a1..an. []
| CoTyApps [Type] -- [] t1 .. tn
| CoLams [Id] -- \x1..xn. []; the xi are dicts or coercions
| CoTyLams [TyVar] -- \a1..an. []