Goal:
  
  A : Type
  B : Type
  P : B → A → A → Type
  idx0 : list B
  idx : sigma (λ _ : list A, list A)
  a : OnOne2All P (pr1 {| pr1 := idx0; pr2 := idx |})
        (pr1 (pr2 {| pr1 := idx0; pr2 := idx |}))
        (pr2 (pr2 {| pr1 := idx0; pr2 := idx |}))
  b : sigma
        (λ index : sigma (λ _ : list B, sigma (λ _ : list A, list A)),
           OnOne2All P (pr1 index) (pr1 (pr2 index)) (pr2 (pr2 index)))
  e : NoConfusion_OnOne2All A B P
        {| pr1 := {| pr1 := idx0; pr2 := idx |}; pr2 := a |} b
  ============================
   (noConfusion_OnOne2All_obligation_2 A B P
      {| pr1 := {| pr1 := idx0; pr2 := idx |}; pr2 := a |} b
      (noConfusion_OnOne2All_obligation_1 A B P
         {| pr1 := {| pr1 := idx0; pr2 := idx |}; pr2 := a |} b e) = e)


DEBUG:Going to execute:
CoreTactics.destruct_sigma idx
Level 5: evaluation returns
idtac of type tacvalue