list sort( s, j )
    list s;
    int j;
    
    {
    int i;
    list head[M], t;
    struct rec aux;
    extern list Last;
    if (s==NULL) return(s);
    if ( s->next == NULL ) {Last = s; return(s);}
    if ( j>D )    {
        for (Last=s; Last->next!=NULL; Last = Last->next);
        return( s );
        }
    for (i=0; i<M; i++) head[i] = NULL;
    /*** place records in buckets ***/
    while (s != NULL) {
        i = charac( j, s->k );
        t = s;
        s = s->next;
        t->next = head[i];
        head[i] = t;
        }
    /*** sort recursively ***/
    t = &aux;
    for (i=0; i<M; i++)  
        if (head[i]!=NULL) {
             t->next = sort( head[i], j+1 );
             t = Last;
        }
    return(aux.next);
    }