Goal:
    A : Type  P : list A → A → Type  b : All_fold P []
  ============================
   (let H := CoreTactics.block in
    NoConfusionHom_All_fold A P [] (All_fold_nil P) b
    → let H0 := CoreTactics.block in All_fold_nil P = b)


DEBUG:Going to execute:
get_signature_pack id id'; hnf in (value of id')