title: Module 'ui.router' is not available
body: <p>I`m new in AngularJS</p>
  
  <p>I`m getting this error: </p>
  
  <pre><code>Uncaught Error: [$injector:modulerr] Failed to instantiate module app due to:
  Error: [$injector:modulerr] Failed to instantiate module ui.router due to:
  Error: [$injector:nomod] Module 'ui.router' is not available! You either misspelled the module name or forgot to load it. If registering a module ensure that you specify the dependencies as the second argument.
  </code></pre>
  
  <p>this is index.html file:</p>
  
  <pre><code>&lt;!doctype html&gt;
  &lt;html ng-app="app"&gt;
      &lt;head&gt;
          &lt;link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/css/bootstrap.min.css"&gt;
          &lt;meta charset="utf-8"&gt;
          &lt;meta name="description" content=""&gt;
          &lt;meta name="viewport" content="width=device-width, initial-scale=1"&gt;
          &lt;title&gt;Untitled&lt;/title&gt;
          &lt;link rel="stylesheet" href="css/style.css"&gt;
          &lt;link rel="author" href="humans.txt"&gt;
  
  
  
      &lt;/head&gt;
      &lt;body ng-controller="FirstCtrl"&gt;
  
      &lt;input type="text" ng-model="first.greeting"/&gt;
      &lt;div ng-class="first.greeting"&gt;{{first.greeting}}&lt;/div&gt;
  
  
  
      &lt;script src="angular.js"&gt;&lt;/script&gt;
      &lt;script src="app/app.js"&gt;&lt;/script&gt;
      &lt;script src="js/main.js"&gt;&lt;/script&gt;
      &lt;/body&gt;
  &lt;/html&gt;
  </code></pre>
  
  <p>and this is app.js file:</p>
  
  <pre><code>var app = angular.module("app", ["ui.router"]).controller("FirstCtrl", function FirstCtrl(){
              var first = this;
              first.greeting = "First";
          });
  </code></pre>
  
  <p>Please help me to solve this issue</p>