T17567StupidTheta.hs:1:37: warning: [-Wdeprecated-flags (in -Wdefault)]
    -XDatatypeContexts is deprecated: It was widely considered a misfeature, and has been removed from the Haskell language.

T17567StupidTheta.hs:6:1: error: [GHC-16220]
    • Uninferrable type variable k0 in
      the datatype context:
      forall (a :: k -> k0). (a b :: k0) ~ (a c :: k0)
    • In the data declaration for ‘T’