Goal:
  
  A : Type
  B : Type
  P : B → A → A → Type
  a : sigma
        (λ index : sigma (λ _ : list B, sigma (λ _ : list A, list A)),
           OnOne2All P (pr1 index) (pr1 (pr2 index)) (pr2 (pr2 index)))
  ============================
   (noConfusion_OnOne2All_obligation_1 A B P a a
      (noConfusion_OnOne2All_obligation_2 A B P a a eq_refl) = eq_refl)


DEBUG:Going to execute:
match type of id with
           | sigma ?P =>
               let idx := fresh "idx" in
               destruct id as [idx id]; repeat CoreTactics.destruct_sigma idx;
                simpl in id
           | _ => idtac
           end