<h3>difference function</h3>
Returns a geometry that represents that part of geometry a that does not intersect with geometry b.

<h4>Syntax</h4>
<pre>difference( a, b )</pre>

<h4>Arguments</h4>
geometry &rarr; geometry
geometry &rarr; geometry

<h4>Example</h4>
<pre> geomToWKT( difference( geomFromWKT( 'LINESTRING(3 3 , 4 4 , 5 5)' ) , geomFromWKT( 'LINESTRING(3 3 , 4 4)' ))  )   &rarr; returns LINESTRING(4 4, 5 5)</pre>