(: Duration: For each employee, show the longest period during which he/she went 
             with no change in salary and his/her salary during that time. :)

declare function local:difference($e,$s, $salary) {
let $n := (xs:date($e) - xs:date($s))
return element difference{element days{xs:integer(fn:replace(xs:string($n),"P|D",""))},element end{ xs:date($e)},element start{ xs:date($s)}, $salary}
};
declare function local:init() {
   for $r in doc("v-emps.xml")/employees/employee
   return (element emp{element diff{ 
             (for $d in $r/salary 
             order by local:difference($d/@tend, $d/@tstart, $d) ascending
             return 
              (local:difference($d/@tend, $d/@tstart, $d), $r/empno))}})
};

declare function local:final_call() {
let $diff := local:init()
for $d in $diff/diff
return (element entry{$d/difference[days=max($d/difference/days)]/days,$d/difference[days=max($d/difference/days)]/salary, $d/empno[1]})
};

let $final := local:final_call()
return element all_entries{$final}