Goal:
  
  A : Type
  B : Type
  C : Type
  P : nat → A → B → Type
  Q : B → C → Type
  R : nat → A → C → Type
  S : nat → A → C → Type
  l'' : list C
  n : nat
  b : All2 Q [] l''
  c : All2i R n [] l''
  H : ∀ (n : nat) (x : A) (y : B) (z : C),
        P n x y → Q y z → R n x z → S n x z
  ============================
   (All2i S n [] l'')


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 := b
       of type
       constr
of type
tacvalue
H := b
of type
constr of type tacvalue