Goal:
  
  A : Type
  B : Type
  C : Type
  P : nat → A → B → Type
  Q : B → C → Type
  R : B → C → Type
  l'' : list C
  n : nat
  x : A
  y : B
  l : list A
  r : list B
  r0 : P n x y
  X : All2i P (S n) l r
  IHX : ∀ l'' : list C,
          All2 Q r l''
          → (∀ (n : nat) (x : A) (y : B) (z : C), P n x y → Q y z → R y z)
            → All2 R r l''
  H : All2 Q (y :: r) l''
  H0 := {| pr1 := {| pr1 := y :: r; pr2 := l'' |}; pr2 := H |}
     : sigma
         (λ index : sigma (λ _ : list B, list C),
            All2 Q (pr1 index) (pr2 index))
  H1 := {| pr1 := y :: r; pr2 := l'' |} : sigma (λ _ : list B, list C)
  H2 := H
     : (λ index : sigma (λ _ : list B, list C),
          All2 Q (pr1 index) (pr2 index)) H1
  ============================
   (let H := CoreTactics.block in
    let H0 := CoreTactics.block in
    (∀ (n : nat) (x : A) (y : B) (z : C), P n x y → Q y z → R y z)
    → All2 R (y :: r) l'')


DEBUG:Going to execute:
generalize (eq_refl : t = id'1); clearbody id'2 id'1; clear id' id;
            try unfold signature in id'2; hnf in id'2; 
            simpl in id'2; rename id'2 into id; cont id id id'1 t
Level 2: Backtrace:

H is used in conclusion.
Level 2: Backtrace:

H is used in conclusion.
Level 2: Backtrace:

H is used in conclusion.
Level 2: Backtrace:

H is used in conclusion.
Level 2: Backtrace:

H is used in conclusion.
Level 2: Backtrace:

H is used in conclusion.
Level 2: Backtrace:

H is used in conclusion.
Level 2: Backtrace:

H is used in conclusion.
Level 2: Backtrace:

H is used in conclusion.
Level 2: Backtrace:

H is used in conclusion.
Level 2: Backtrace:

H is used in conclusion.
Level 2: Backtrace:

H is used in conclusion.