let rec insere_exp s l t sign =
match l with
| (tt,si2)::fin -> ( match comp s t tt with
| 0 -> if sign = si2 then (t,sign)::(tt,si2)::fin else fin
| x ->
if x<0 then
(t,sign)::l
else (tt,si2)::(insere_exp s fin t sign) )
| [] -> [t,sign]