let student_to_xml (s:student) =
let attrs = [("nom",s.name);("pre",s.pren);("login",s.login)] in
let fteams = List.filter (fun t -> (t.r != Zero)) (H.assoc_to_list s.teams) in
let steams = List.sort (fun u v -> compare u.proj v.proj) fteams in
let xteams = List.map steam_to_xml steams in
Xml.Element ("student",attrs,xteams)