title: Firebase (4.0.0): Use of unresolved identifier FirebaseApp when installing FirebaseDatabase
body: <p>This is what happens:</p>
  
  <ul>
  <li>running on Xcode Version 7.3.1 (7D1014)</li>
  <li>pod 'Firebase/Core'</li>
  <li>import Firebase in the Class</li>
  </ul>
  
  <p><a href="https://i.stack.imgur.com/zHW6c.png" rel="noreferrer">unresolved on Database</a></p>
  
  <p>Then I added the Database framework</p>
  
  <ul>
  <li>pod 'Firebase/Core'</li>
  <li>pod 'Firebase/Database'</li>
  </ul>
  
  <p><a href="https://i.stack.imgur.com/kUsTn.png" rel="noreferrer">unresolved on FirebaseApp</a></p>
  
  <p>It seems that the 2 frameworks are in mutex mode. They cannot coexist.</p>
  
  <p>I have tried everything: update, install, uninstall, recreate the project, recreate the workspace. All.</p>
  
  <p>May you help me. Is there a bug on last Firebase release?</p>