Sum of identical nodes

Hi,

Sorry for this repost... but I needed some help with this. Any help is
greatly appreciated. Below is an example of what I hope to acheive

In this example, my input files are File1 and File2 and wish to output
my result to File3
- add 1 from File1/AAA to 2 from File2/AAA to output File3
- add 2 from File1/AAA to 3 from File2/AAA to output File3
- add 2 from File1/BBB to 0 from File2/BBB to output File3
- add 3 from File1/BBB to 0 from File2/BBB to output File3

Each file in File1 and File2 have few hundreds nodes of <moid></moid>
and <mt></mt>. My biggest hindrance is how to recursively sum up each
node from each nodeset.


File 1:
<xml>
<moid> AAA </moid>
    <mt> 1 </mt>
    <mt> 2 </mt>
<moid> BBB </moid>
    <mt> 2 </mt>
    <mt> 3 </mt>
</xml>

File 2:
<xml>
<moid> AAA </moid>
    <mt> 2 </mt>
    <mt> 3 </mt>
<moid> BBB </moid>
    <mt> 0 </mt>
    <mt> 0 </mt>
</xml>

File 3:
<xml>
<moid> AAA </moid>
    <mt> 3 </mt>
    <mt> 5 </mt>
<moid> BBB </moid>
    <mt> 2 </mt>
    <mt> 3 </mt>
</xml>