Goal:
  
  A : Type
  P : list A → A → Type
  d : A
  Γ : list A
  a : All_fold P Γ
  p : P Γ d
  b : All_fold P (d :: Γ)
  ============================
   (NoConfusionHom_All_fold A P (d :: Γ) (All_fold_cons P a p) b
    → let H := CoreTactics.block in All_fold_cons P a p = b)


DEBUG:Going to execute:
idtac
Level 12: id'
 has value 
b