Goal:
  
  A : Type
  P : nat → A → Type
  n : nat
  x : A
  Γ : list A
  IHΓ : All_fold (λ (Γ : list A) (d : A), P (n + #|Γ|) d) (List.rev Γ)
        → Alli P n Γ
  a : All_fold (λ (Γ : list A) (d : A), P (n + #|Γ|) d) (x :: List.rev Γ)
  ============================
   (Alli P n (Γ ++ [x]))


DEBUG:Going to execute:
DepElim.do_intros H; DepElim.generalize_by_eqs H
Level 1: evaluation returns
DepElim.do_intros H; DepElim.generalize_by_eqs H; tac H
where
tac := fun hyp => DepElim.do_case hyp
       where
       id := a
       of type
       ident
of type
tacvalue
H := a
of type
ident of type tacvalue