private void condense() {
        if ((cut != null) && (plus.cut == null) && (minus.cut == null) &&
            (((plus.attribute == null) && (minus.attribute == null)) ||
             ((plus.attribute != null) && plus.attribute.equals(minus.attribute)))) {
            attribute = (plus.attribute == null) ? minus.attribute : plus.attribute;
            cut       = null;
            plus      = null;
            minus     = null;
        }
    }