T7453.hs:10:30: error:
    Couldn't match expected type ‘t1’ with actual type ‘t’
      because type variable ‘t1’ would escape its scope
    This (rigid, skolem) type variable is bound by
      the type signature for: z :: Id t1
      at T7453.hs:8:16-19
    In the first argument of ‘Id’, namely ‘v’
    In the expression: Id v
    Relevant bindings include
      aux :: Id t1 (bound at T7453.hs:10:21)
      z :: Id t1 (bound at T7453.hs:9:11)
      v :: t (bound at T7453.hs:7:7)
      cast1 :: t -> a (bound at T7453.hs:7:1)

T7453.hs:16:33: error:
    Couldn't match expected type ‘t2’ with actual type ‘t’
      because type variable ‘t2’ would escape its scope
    This (rigid, skolem) type variable is bound by
      the type signature for: z :: () -> t2
      at T7453.hs:14:16-22
    In the first argument of ‘const’, namely ‘v’
    In the expression: const v
    Relevant bindings include
      aux :: b -> t2 (bound at T7453.hs:16:21)
      z :: () -> t2 (bound at T7453.hs:15:11)
      v :: t (bound at T7453.hs:13:7)
      cast2 :: t -> t1 (bound at T7453.hs:13:1)

T7453.hs:21:15: error:
    Couldn't match expected type ‘t2’ with actual type ‘t’
      because type variable ‘t2’ would escape its scope
    This (rigid, skolem) type variable is bound by
      the type signature for: z :: t2
      at T7453.hs:20:16
    In the expression: v
    In an equation for ‘z’:
        z = v
          where
              aux = const v
    Relevant bindings include
      aux :: forall b. b -> t2 (bound at T7453.hs:22:21)
      z :: t2 (bound at T7453.hs:21:11)
      v :: t (bound at T7453.hs:19:7)
      cast3 :: t -> t1 (bound at T7453.hs:19:1)