changed :-( *)
w#hadjustment#set_value w#hadjustment#upper;
w#hadjustment#set_value w#hadjustment#lower;
+ w#vadjustment#set_value w#vadjustment#lower;
w#vadjustment#set_value
(w#vadjustment#upper -. w#vadjustment#page_size));
with Not_found -> assert false)