Goal:
  
  A : Type
  P : A → A → Type
  a : sigma
        (λ index : sigma (λ _ : list A, list A),
           OnOne2 P (pr1 index) (pr2 index))
  ============================
   (noConfusion_OnOne2_obligation_1 A P a a
      (noConfusion_OnOne2_obligation_2 A P a a eq_refl) = eq_refl)


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