@Override
    public String toString() {
      if (this == TRUE) return "Cond.TRUE";
      if (this == FALSE) return "Cond.FALSE";
      StringBuilder sb = new StringBuilder("Cond{");
      for (Cond<T> c = this; c != null; c = c.next) {
        sb.append(JBIterator.toShortString(c.impl));
        if (c.next != null) sb.append(", ");
      }
      return sb.append("}").toString();
    }
@Override
    public String toString()