Goal:
  
  A : Type
  B : Type
  C : Type
  D : Type
  E : Type
  P : E → A → Type
  Q : C → A → Type
  R : B → D → Type
  f : B → C → E
  b : B
  l : list B
  l''' : list D
  hb : All2 R (b :: l) l'''
  x : C
  y : A
  l0 : list C
  l' : list A
  r : Q x y
  ha : All2 Q l0 l'
  H : #|l| = #|l0|
  hPQ : ∀ (x : B) (y : C) (z : A) (w : D), R x w → Q y z → P (f x y) z
  IHha : ∀ (l : list B) (l''' : list D),
           All2 R l l''' → #|l| = #|l0| → All2 P (map2 f l l0) l'
  ============================
   (All2 P (map2 f (b :: l) (x :: l0)) (y :: l'))


DEBUG:Going to execute:
DepElim.do_depelim_nosimpl tac H; DepElim.simpl_dep_elim
Level 3: evaluation returns
DepElim.do_depelim_nosimpl tac H; DepElim.simpl_dep_elim;
 CoreTactics.unblock_goal
where
tac := fun hyp => DepElim.do_case hyp
       where
       id := hb
       of type
       constr
of type
tacvalue
H := hb
of type
constr of type tacvalue

Level 2: evaluation returns
DepElim.do_depelim_nosimpl tac H; DepElim.simpl_dep_elim;
 CoreTactics.unblock_goal
where
tac := fun hyp => DepElim.do_case hyp
       where
       id := hb
       of type
       constr
of type
tacvalue
H := hb
of type
constr of type tacvalue

Level 1: evaluation returns
DepElim.do_depelim_nosimpl tac H; DepElim.simpl_dep_elim;
 CoreTactics.unblock_goal
where
tac := fun hyp => DepElim.do_case hyp
       where
       id := hb
       of type
       constr
of type
tacvalue
H := hb
of type
constr of type tacvalue