edit :-
	edit(file([],[])).
        
edit(File) :-
        read(Command),
        edit(File,Command).

edit(_File,exit) :- !.
edit(File,Command) :-
        apply(Command,File,File1),
        !,
        edit(File1).
edit(File,Command) :-
        write(Command),
        write(' is not applicable'),
        !,
        edit(File).

apply(up,file([X|Xs],Ys),file(Xs,[X|Ys])).

apply(down,file(Xs,[Y|Ys]),file([Y|Xs],Ys)).

apply(insert(Line),file(Xs,Ys),file(Xs,[Line|Ys])).

apply(delete,file(Xs,[_Y|Ys]),file(Xs,Ys)).

apply(print,file([X|Xs],Ys),file([X|Xs],Ys)) :-
	write(X), nl.
apply(print(*),file(Xs,Ys),file(Xs,Ys)) :-
        reverse(Xs,Xs1),
        write_file(Xs1),
        write_file(Ys).

write_file([X|Xs]) :-
        write(X), nl, write_file(Xs).
write_file([]).

sublist(Xs,Ys) :-
	append(_,Xs,Zs),
	append(Zs,_,Ys).