T4179.hs:26:16: error:
    • Couldn't match type ‘A3 (x (A2 (FCon x) -> A3 (FCon x)))’
                     with ‘A3 (FCon x)’
      Expected type: x (A2 (FCon x) -> A3 (FCon x))
                     -> A2 (FCon x) -> A3 (FCon x)
        Actual type: x (A2 (FCon x) -> A3 (FCon x))
                     -> A2 (x (A2 (FCon x) -> A3 (FCon x)))
                     -> A3 (x (A2 (FCon x) -> A3 (FCon x)))
      NB: ‘A3’ is a type function, and may not be injective
    • In the first argument of ‘foldDoC’, namely ‘op’
      In the expression: foldDoC op
      In an equation for ‘fCon’: fCon = foldDoC op
    • Relevant bindings include
        fCon :: Con x -> A2 (FCon x) -> A3 (FCon x)
          (bound at T4179.hs:26:1)