s, a function's 
postconditions may no longer be true by the time the function returns to the 
caller.</p>
<blockquote>
<p><b><i>Explanation: </i></b>The state of files and directories is often
globally shared, and thus may be changed unexpectedly by other threads, 
processes, or even other computers having network access to the filesystem. As an 
example of the difficulties this can cause, note that the following asserts 
may fail:</p>
<blockquote>
<p><code>assert( exists( &quot;foo&quot; ) == exists( &quo