anchor.diff:      it controls the lifetime of the `MissionService`.
   :marked
     The *History* log demonstrates that messages travel in both directions between
  -  the parent `MissionControlComponent` and the `AstronoutComponent` children,
  +  the parent `MissionControlComponent` and the `AstronautComponent` children,
     facilitated by the service:
     
   figure.image-display
  
positive.code: :marked
    ### Test it
    
    Tests click buttons of both the parent `MissionControlComponent` and the `AstronoutComponent` children
    and verify that the *History* meets expectations:
    
  +makeExample('cb-component-communication/e2e-spec.js', 'bidirectional-service')
  
negative.code: +makeExample('cb-component-communication/ts/app/missioncontrol.component.ts')
  
  :marked
    The `AstronautComponent` also injects the service in its constructor.
    Each `AstronautComponent` is a child of the `MissionControlComponent` and therefore receives its parent's service instance:
    
  +makeExample('cb-component-communication/ts/app/astronaut.component.ts')
  
  