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)))
  ============================
   (NoConfusion_OnOne2i A P a a)


DEBUG:Going to execute:
CoreTactics.destruct_sigma id
Level 4: evaluation returns
CoreTactics.destruct_sigma id; destruct id
where
id := a
of type
constr of type tacvalue