skaller wrote:
>  
>> It works ! ... Or did I miss something ?
>>     
>
> Yes. Read the manual: the ordered type mandates a total order.
>
> Just because the Ocaml type system is too weak too represent this
> constraint does not remove your obligation to meet it.
>
> Whether or not it happens to work with the current implementation
> isn't relevant.  
>
>   

Ok...
Still, using the current implementation (even if it means making a 
copy!) should be an efficient solution!

:-)