TidyClassKinds.hs:13:10: error:
    • Illegal instance declaration for
        ‘Poly @{k -> *} @{k -> *} (ProxySyn @{k}) (ProxySyn @{k})’
        (All instance types must be of the form (T t1 ... tn)
         where T is not a synonym.
         Use TypeSynonymInstances if you want to disable this.)
    • In the instance declaration for ‘Poly ProxySyn ProxySyn’