public static Keyword tryGoalComplementProof(ControlFrame frame) {
    { Description description = ControlFrame.extractSubgoalDescriptionOfFrame(frame);
      Description complement = Description.getInferableComplementDescription(description);
      ControlFrame downframe = ControlFrame.createSubgoalFrame(frame, null, Logic.KWD_ALL_SUBGOAL_STRATEGIES);

      KeyValueList.setDynamicSlotValue(downframe.dynamicSlots, Logic.SYM_LOGIC_DESCRIPTION, complement, null);
      downframe.reversePolarityP = false;
      return (Logic.KWD_MOVE_DOWN);
    }
  }