Goal:
  
  G : t
  idx : sigma (fun _ : VSet.t => sigma (fun _ : V.t => V.t))
  a : SPath (pr1 idx) (pr1 (pr2 idx)) (pr2 (pr2 idx))
  ============================
   (noConfusion_SPath_obligation_1 {| pr1 := idx; pr2 := a |}
      {| pr1 := idx; pr2 := a |}
      (noConfusion_SPath_obligation_2 {| pr1 := idx; pr2 := a |}
         {| pr1 := idx; pr2 := 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