let rec add_annot annot acc =
match acc with
| [] -> [annot], true
| a::tl ->
if annot.annot_id < a.annot_id then annot::acc, true
else if annot.annot_id = a.annot_id then acc, false
else
let tl, added = add_annot annot tl in
a::tl, added