let unwrap_sexpr e = match e with
| Sexpr(x) -> x;;
let rec sexpr_mem x = function
    [] -> false
  | Sexpr(a)::l -> (sexpr_eq a x) || sexpr_mem x l
let rec rem_sexpr_dup_assist l new_l = match l with
| [] -> new_l
| hd :: tl -> if(sexpr_mem (unwrap_sexpr hd) new_l) then (rem_sexpr_dup_assist tl new_l) else (rem_sexpr_dup_assist tl (new_l @ [hd]));;
let remove_sexpr_dup l = rem_sexpr_dup_assist l [];;