bubsort(L,S) :-
       append(X,[A,B|Y],L),
       B < A,
       append(X,[B,A|Y],M),
       !,
       bubsort(M,S).
 bubsort(L,L).
 
 append([],L,L).
 append([H|T],L,[H|V]) :-
       append(T,L,V).
