Goal:
    X1 : sigma (fun _ : t => t)  X : lt_ (pr1 X1) (pr2 X1)
  ============================
   (forall x : t,
    {| pr1 := x; pr2 := x |} = X1 ->
    let H := CoreTactics.block in let H0 := CoreTactics.block in False)


DEBUG:Going to execute:
fun id' =>
             match id' with
             | id => idtac
             | _ => revert id'; CoreTactics.revert_until id
             end