<p><strong>Hashable Objects in Python</strong> Mutable
objects are not hashable.  You might ask why.  Hash function usually
depend on object state.  So if state changes, the hash function
could change, violating the consistency specification.  How do you 
see if something is hashable?  Call the <code>hash</code> function
on it.</p>

<h2>Sets</h2>

<p><strong>A Little Math</strong></p>

<p><strong>Stupid Set (You will later write this in Java)</strong></p>

<p><strong>Hashing and Sets</strong>  Here is why retrieval from
a set is fast.</p>


<h2>Dictionaries</h2>