> When i compile the following program with ocamlc i get a segmentation 
fault. 
> [...]
> If i replace the function LL.add by
> 
>  let rec add a b = match a, b with
>      [], [] -> []
>    | x::a', y::b' -> (R.add x y)::(add a' b')
>    | _ -> failwith "add"
> 
> the segmentation fault magically disappear.

It seems that it is sufficient to define

        let add a b = List.map2 R.add a b

instead of

        let add = List.map2 R.add

to make the segmentation fault disappear (Ocaml 3.09.1).

Sebastian.