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)))
  e : NoConfusion_OnOne2i A P a b
  ============================
   (noConfusion_OnOne2i_obligation_2 A P a b
      (noConfusion_OnOne2i_obligation_1 A P a b e) = e)


DEBUG:Going to execute:
fun a b =>
             CoreTactics.destruct_sigma a; CoreTactics.destruct_sigma b;
              destruct a; DepElim.depelim b; simpl in * |-;
              CoreTactics.on_last_hyp
               ltac:(fun id =>
                       hnf in id;
                        CoreTactics.destruct_tele_eq id || destruct id);
              (solve [ constructor ])