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
  y0 : C
  l' : list C
  n : nat
  x : A
  y : B
  l : list A
  r : list B
  r0 : P n x y
  a : All2i P (Datatypes.S n) l r
  q : Q y y0
  b : All2 Q r l'
  c : All2i R n (x :: l) (y0 :: l')
  c0 := {|
          pr1 := {| pr1 := n; pr2 := {| pr1 := x :: l; pr2 := y0 :: l' |} |};
          pr2 := c
        |}
     : sigma
         (λ index : sigma (λ _ : nat, sigma (λ _ : list A, list C)),
            All2i R (pr1 index) (pr1 (pr2 index)) (pr2 (pr2 index)))
  c1 := {| pr1 := n; pr2 := {| pr1 := x :: l; pr2 := y0 :: l' |} |}
     : sigma (λ _ : nat, sigma (λ _ : list A, list C))
  c2 := c
     : (λ index : sigma (λ _ : nat, sigma (λ _ : list A, list C)),
          All2i R (pr1 index) (pr1 (pr2 index)) (pr2 (pr2 index))) c1
  ============================
   (let H := CoreTactics.block in
    (∀ (n : nat) (x : A) (y : B) (z : C), P n x y → Q y z → R n x z → S n x z)
    → (∀ l'' : list C,
         All2 Q r l''
         → All2i R (Datatypes.S n) l l'' → All2i S (Datatypes.S n) l l'')
      → let H0 := CoreTactics.block in All2i S n (x :: l) (y0 :: 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:

c is used in conclusion.
Level 2: Backtrace:

c is used in conclusion.
Level 2: Backtrace:

c is used in conclusion.
Level 2: Backtrace:

c is used in conclusion.
Level 2: Backtrace:

c is used in conclusion.
Level 2: Backtrace:

c is used in conclusion.
Level 2: Backtrace:

c is used in conclusion.
Level 2: Backtrace:

c is used in conclusion.
Level 2: Backtrace:

c is used in conclusion.
Level 2: Backtrace:

c is used in conclusion.
Level 2: Backtrace:

c is used in conclusion.
Level 2: Backtrace:

c is used in conclusion.