<p><em>Taken from Wikipedia, the free encyclopedia:</em></p>

<p>A fundamental property of all hash functions is that if
two hashes (according to the same function) are different,
then the two inputs were different in some way. This property
is a consequence of hash functions being deterministic,
mathematical functions, but they are generally not one-to-one,
with a large domain and smaller range. Consequently, the 
equality of two hash values does not guarantee the two
inputs were the same, but in some cases, probability theoretic
or computability theoretic guarantees apply.</p>
