Goal:
  
  G : t
  idx : sigma (fun _ : VSet.t => sigma (fun _ : V.t => V.t))
  a : SPath (pr1 idx) (pr1 (pr2 idx)) (pr2 (pr2 idx))
  b : sigma
        (fun index : sigma (fun _ : VSet.t => sigma (fun _ : V.t => V.t)) =>
         SPath (pr1 index) (pr1 (pr2 index)) (pr2 (pr2 index)))
  H : NoConfusion_SPath {| pr1 := idx; pr2 := a |} b
  ============================
   ({| pr1 := idx; pr2 := a |} = b)


DEBUG:Going to execute:
let idx := fresh "idx" in
           destruct id as [idx id]; repeat CoreTactics.destruct_sigma idx;
            simpl in id
DEBUG LTAC Evaluated term: idx
DEBUG LTAC Evaluated term: (sigma
                              (fun _ : VSet.t => sigma (fun _ : V.t => V.t)))
Level 6: type of id
 has value 
(sigma (fun _ : VSet.t => sigma (fun _ : V.t => V.t)))