Goal:
  
  A : Type
  P : list A → A → Type
  d : A
  Γ : list A
  a : All_fold P Γ
  p : P Γ d
  ============================
   (eq_refl = eq_refl)


DEBUG:Going to execute:
match goal with
           | |- ?x = ?y =>
                 let x' := eval hnf in x in
                 let y' := eval hnf in y in
                 change_no_check (x' = y')
           end