title: What is the difference between these functions?
body: <p>I have the book Jquery in Action, and it mentions these three functions when talking about removing conflict with other libraries. However, I don't know what the difference is between them and do not understand the book's explanation.</p>
  
  <pre><code>jQuery(function($) {
      alert('I"m ready!');
  });
  
  var $ = 'Hi!';
  jQuery(function() {
      alert('$ = ' + $);
  });
  
  var $ = 'Hi!';
  jQuery(function($) {
      alert('$ = ' + $);
  });
  </code></pre>
  
  <p>Does anyone know what the difference is? Thanks.</p>