let minus_v_element = {
  el_id = get_unique_element_id ();
  el_literal = Term.minus_v;
  el_choice_point = State.valid_choice_point;
  el_pars = Term.vars_of_literal Term.minus_v;
  el_generation = 0;
  el_is_fd_incomplete = false;
  el_compacted = -1;
}