let rec list_of_string_aux s n = 
    if String.length s = n then []
        else (String.get s n)::(list_of_string_aux s (n+1));;

let rec list_of_string s =  list_of_string_aux s 0;;

let rec filtre m1 m2 = 
    match(m1,m2) with
      ([],[])      -> true
    | (t1::r1,[])  -> false
    | ([],t2::r2)  -> false
    | (t1::r1,t2::r2) -> ((t1=t2 or t2='?') & (filtre r1 r2)) or
                         ((t2='*') & (filtre r1 (t2::r2))) or 
                         ((t2='*') & (filtre (t1::r1) r2));;