<h3>symDifference function</h3>
Returns a geometry that represents the portions of a and b that do not intersect.

<h4>Syntax</h4>
<pre>symDifference( geometry a, geometry b)</pre>

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

<h4>Example</h4>
<pre> geomToWKT( symDifference(  geomFromWKT( 'LINESTRING(3 3 , 4 4 , 5 5)' ) , geomFromWKT( 'LINESTRING(3 3 , 8 8)' ))   )   &rarr; returns LINESTRING(5 5, 8 8)</pre>
