extremum(L,Min,Max):-
  min_list(L,Min),
  max_list(L,Max),
  !.

copy(File1,File2):-
    open(File1, read, In),
    open(File2, write, Out),
    get_char(In, Char),
    copy_stream(Char, In, Out),
    close(In),
    close(Out).

copy_stream(end_of_file, _, _):- !.
copy_stream(Char, In, Out):-
    put_char(Out, Char),
    get_char(In, Char2),
    copy_stream(Char2, In, Out).