T15795.hs:12:3: error:
    • Cannot generalise type; skolem ‘k’ would escape its scope
      if I tried to quantify (a0 :: k) in this type:
        forall k (b :: k). T @k @a0 b
      (Indeed, I sometimes struggle even printing this correctly,
       due to its ill-scoped nature.)
    • In the definition of data constructor ‘MkT’
      In the data declaration for ‘T’