anchor.diff:    :marked
       The real problem is that there are _two different classes_ trying to do the same thing.
       
  -    真正的问题在于，有_两个不同的类_视图做同一件事。
  +    真正的问题在于，有_两个不同的类_试图做同一件事。
   
       It's OK to import the _same_ directive class multiple times. 
       Angular removes duplicate classes and only registers one of them.
  
positive.code:   * create an `app/core` folder
    * 创建`app/core`文件夹
    * move the `UserService` and `TitleComponent` from `app/` to `app/core`
    * 把`UserService`和`TitleComponent`从`app`移到`app`中
    * create a `CoreModule` class to own the core material
    * 创建一个`CoreModule`类来管理这些核心素材
    * update the `AppRoot` module to  import `CoreModule`
  
negative.code:   
    `CrisisModule`和本模块非常像，我们不再赘述。
  
    <live-example embedded plnkr="pre-shared.3" img="devguide/ngmodule/v3-plunker.png">试试在线例子。</live-example>
  
  a#shared-module
  