"Outer join" for XSLT?

I'm having troubling finding a means of producing the difference between two node sets with identical structures. 

Given:
<r>
 <e>1</e>
 <e>2</e>
 <e>3</e>
 <e>4</e>
 <e>5</e>
</r>

and 

<r>
 <e>2</e>
 <e>4</e>
</r>

What I'd like to produce is:

<r>
 <e>1</e>
 <e>3</e>
 <e>5</e>
</r>

What I'm looking to do is analogous to a SQL outer-join. It may simply be that I don't know the term to search for.

Using XSLT 2.0, how is this done?

-- 
Charles Knell
cknell@xxxxxxxxxx - email