How is satisfies different from where ?

[David]

I've embarised to admit I've never used the sum/satisfies expressions in 
XQuery.
Im trying to grok this recently posted pastebin
http://pastebin.com/7GGQxpYH

quote----
let $result1 := ( some $i in (1 to 5), $j in (5 to 10)
   satisfies $j - $i = 0 )
let $result2 := ( some $i in (1 to 5), $j in (6 to 10)
   satisfies $j - $i = 0 )
return
<test>
<result1>{$result1}</result1>
<result2>{$result2}</result2>
</test>

----

How is this different from

--------
<test>
<result1>{ exists(
for $i in (1 to 5) , $j in (5 to 10)
where $j - $i = 0 return  $i
)}</result1>
<result2>{
exists(
for $i in (1 to 5) ,  $j in (6 to 20)
where $j - $i = 0 return $i
)}</result2>
</test>



---------------

More generaly what does satisfies/sum do differently then for/where ?
Is it simply a shorter version of the same ? or is there a operaitonal 
difference ?
Where would I want to use some/satisfies where for/where is either 
inappropreate or clumbsy ?



Thanks for any insight







-- 
-------------------------
David A. Lee
http://x-query.com/mailman/listinfo/talk
http://www.calldei.com
http://www.xmlsh.org