What is the difference between these functions?
<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>
