Goal:
    A : Type  P : list A → A → Type  x : A  a : All_fold P [x]
  ============================
   (let H := CoreTactics.block in P [] x)


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