
T5300.hs:15:9:
    Ambiguous type variable `c0' in the constraint:
      (C1 a1 b2 c0) arising from a use of `f1'
    Probable fix: add a type signature that fixes these type variable(s)
    In the first argument of `(>>=)', namely `f1 fm'
    In the expression: f1 fm >>= return . undefined
    In an equation for `f2': f2 fm = f1 fm >>= return . undefined
