title: 3 duplicated symbols for architecture i386
body: <p>After I try to build my app with Xcode, this error appear:</p>
  
  <pre><code>     duplicate symbol _OBJC_IVAR_$_StoreVars._Traguardo in:
      /Users/Fede/Library/Developer/Xcode/DerivedData/ProvaTapChallenge-bqumsaqmowwbdfbzgzrrwlblxsgh/Build/Intermediates/ProvaTapChallenge.build/Debug-iphonesimulator/ProvaTapChallenge.build/Objects-normal/i386/ViewController.o
      /Users/Fede/Library/Developer/Xcode/DerivedData/ProvaTapChallenge-bqumsaqmowwbdfbzgzrrwlblxsgh/Build/Intermediates/ProvaTapChallenge.build/Debug-iphonesimulator/ProvaTapChallenge.build/Objects-normal/i386/ViewControllerBase.o
  duplicate symbol _OBJC_METACLASS_$_StoreVars in:
      /Users/Fede/Library/Developer/Xcode/DerivedData/ProvaTapChallenge-bqumsaqmowwbdfbzgzrrwlblxsgh/Build/Intermediates/ProvaTapChallenge.build/Debug-iphonesimulator/ProvaTapChallenge.build/Objects-normal/i386/ViewController.o
      /Users/Fede/Library/Developer/Xcode/DerivedData/ProvaTapChallenge-bqumsaqmowwbdfbzgzrrwlblxsgh/Build/Intermediates/ProvaTapChallenge.build/Debug-iphonesimulator/ProvaTapChallenge.build/Objects-normal/i386/ViewControllerBase.o
  duplicate symbol _OBJC_CLASS_$_StoreVars in:
      /Users/Fede/Library/Developer/Xcode/DerivedData/ProvaTapChallenge-bqumsaqmowwbdfbzgzrrwlblxsgh/Build/Intermediates/ProvaTapChallenge.build/Debug-iphonesimulator/ProvaTapChallenge.build/Objects-normal/i386/ViewController.o
      /Users/Fede/Library/Developer/Xcode/DerivedData/ProvaTapChallenge-bqumsaqmowwbdfbzgzrrwlblxsgh/Build/Intermediates/ProvaTapChallenge.build/Debug-iphonesimulator/ProvaTapChallenge.build/Objects-normal/i386/ViewControllerBase.o
  ld: 3 duplicate symbols for architecture i386
  clang: error: linker command failed with exit code 1 (use -v to see invocation)
  </code></pre>
  
  <p>how can i solve this? help me, please!</p>