1·Sometimes the code is very obviously unreachable (uncalled private methods, unread local variables, and so forth).
有时候，这些代码是明显不可达的(未调用的私有方法以及未读入的本地变量，等等)。
2·Active state means the Connection Manager activates the service; defined is equivalent to down, in which case the Connection Manager does not start the service, making it unreachable.
active状态意味着Connection Manager激活服务；defined状态相当于停止状态，在此状态下，Connection Manager不启动服务，使之不可达。
3·It not only used pre-image computation to avoid false negative, but also incorporated reachable states and unreachable states in the verification process.
除了利用原像计算避免误判之外，该算法还将可达状态和不可达状态引入到验证过程中。
4·A destination unreachable error PDU was received.
收到了一个目的地不可达的PD U协议数据单元错误。