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


DEBUG:Going to execute:
fun tac => lazymatch goal with
                      | H:_ |- _ => tac H
                      end