Goal:
  
  A : Type
  P : A → A → Type
  idx0 : list A
  idx : list A
  a : OnOne2 P (pr1 {| pr1 := idx0; pr2 := idx |})
        (pr2 {| pr1 := idx0; pr2 := idx |})
  b : sigma
        (λ index : sigma (λ _ : list A, list A),
           OnOne2 P (pr1 index) (pr2 index))
  H : NoConfusion_OnOne2 A P
        {| pr1 := {| pr1 := idx0; pr2 := idx |}; pr2 := a |} b
  ============================
   ({| pr1 := {| pr1 := idx0; pr2 := idx |}; pr2 := a |} = b)


DEBUG:Going to execute:
idtac
DEBUG LTAC Evaluated term: idx
DEBUG LTAC Evaluated term: (list A)
Level 6: type of id
 has value 
(list A)