mkClassPPredCoI :: Class -> [Type] -> [CoercionI] -> CoercionI
-- mkClassPPredCoI cls tys cois = coi
-- coi : PredTy (cls tys) ~ predTy (cls (tys `cast` cois))
mkClassPPredCoI :: Class -> [Type] -> [CoercionI] -> CoercionI
-- mkClassPPredCoI cls tys cois = coi
-- coi : PredTy (cls tys) ~ predTy (cls (tys `cast` cois))