unique-sequence-numbering

Sorry for reposting..The subject was wrong!!
i have an xml file which looks like below.
<?xml version="1.0"?>
<students>
	<student id = "101">
		<name>A</name>
		<address>XXX</address>
	</student>
	<student id = "201">
		<name>B</name>
		<address>YYY</address>
	</student>
	<student id = "301">
		<name>C</name>
		<address>XXX</address>
	</student>
	<student id = "401">
		<name>E</name>
		<address>YYY<address>
	</student>
</students>

And i have to deliver a CSV file that has the following fields.

Student-id , SequenceNumber , name, address.

Sequence number is an automatically generated  number ( should start from 1 to 
end of Students )..

so a typical CSV FIle would be..

101,1,A,abc
102,2,B,bcd
103,3,C,cde
104,4,D,efg
..
Now There is a business rule that says that if a student has an address value 
that is equal to 'YYY',  then show the complete information *line* twice, with 
only the sequence number changed..
That is
101,1,A,abc
102,2,B,bcd
102,3,B,bcd  <-- repeated again with sequence number changed
103,4,C,cde
104,5,D,efg
104,6,D,efg <-- repeated again with sequence number changed


I am using the position() function to get the serial number..This is where the 
problem starts..
If i put a condition that
 if address == 'YYY' ( just pseudo code. dont mind the syntax )
{
value-of-select --> @id,position(),name,address
		  @id,position()+1,name,address
}
else
{
value-of-select --> @id,position(),name,address
}

I end up getting something like this

101,1,A,abc
102,2,B,bcd
102,3,B,bcd  <-- repeated again with sequence number changed
103,3,C,cde  <-- same sequence number repeated... That is the position ..
104,4,D,efg
104,5,D,efg <-- repeated again with sequence number changed

and what i want should look like

101,1,A,abc
102,2,B,bcd
102,3,B,bcd  <-- repeated again with sequence number changed
103,4,C,cde  <-- this is not showing up position but prev-seq+1
104,5,D,efg
104,6,D,efg <-- repeated again with sequence number changed

so the requirement tells, if you find address equal to 'YYY', then add it show 
it once more with a sequence number -> prev-seq-num +1  and then every 
subsequent sequence number should be consequitive. The sequence number is a 
unique number ( from 1 to End of students ).

I can not think of a way to do this.This looks totally like a dead end to me.
I shall be highly thankful if some one can please help me out of this 
situation...
Please let me know if i am missing out any information that would make the 
question clearer..

Thanks a ton!!!!!!!!! 

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