Goal:
  
  A : Type
  P : nat → A → A → Type
  a : sigma
        (λ index : sigma (λ _ : nat, sigma (λ _ : list A, list A)),
           OnOne2i P (pr1 index) (pr1 (pr2 index)) (pr2 (pr2 index)))
  b : sigma
        (λ index : sigma (λ _ : nat, sigma (λ _ : list A, list A)),
           OnOne2i P (pr1 index) (pr1 (pr2 index)) (pr2 (pr2 index)))
  H : NoConfusion_OnOne2i A P a b
  ============================
   (a = b)


DEBUG:Going to execute:
let idx := fresh "idx" in
           destruct id as [idx id]; repeat CoreTactics.destruct_sigma idx;
            simpl in id
DEBUG LTAC Evaluated term: a
DEBUG LTAC Evaluated term: (sigma
                              (λ index : sigma
                                           (λ _ : nat,
                                              sigma (λ _ : list A, list A)),
                                 OnOne2i P (pr1 index) 
                                   (pr1 (pr2 index)) 
                                   (pr2 (pr2 index))))
Level 4: type of id
 has value 
(sigma
   (λ index : sigma (λ _ : nat, sigma (λ _ : list A, list A)),
      OnOne2i P (pr1 index) (pr1 (pr2 index)) (pr2 (pr2 index))))