Goal:
  
  A : Type
  P : A → A → Type
  a : sigma
        (λ index : sigma (λ _ : list A, list A),
           OnOne2 P (pr1 index) (pr2 index))
  b : sigma
        (λ index : sigma (λ _ : list A, list A),
           OnOne2 P (pr1 index) (pr2 index))
  e : NoConfusion_OnOne2 A P a b
  ============================
   (noConfusion_OnOne2_obligation_2 A P a b
      (noConfusion_OnOne2_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 ])