Goal:
  
  G : t
  idx0 : VSet.t
  idx : sigma (fun _ : V.t => V.t)
  a : SPath (pr1 {| pr1 := idx0; pr2 := idx |})
        (pr1 (pr2 {| pr1 := idx0; pr2 := idx |}))
        (pr2 (pr2 {| pr1 := idx0; pr2 := idx |}))
  ============================
   (NoConfusion_SPath {| pr1 := {| pr1 := idx0; pr2 := idx |}; pr2 := a |}
      {| pr1 := {| pr1 := idx0; pr2 := idx |}; pr2 := a |})


DEBUG:Going to execute:
CoreTactics.destruct_sigma idx