(VAR f l x xs y )
(RULES 
        app(rev,nil) -> nil
        app(rev,app(app(cons,x),l)) -> app(app(cons,app(app(rev1,x),l)),app(app(rev2,x),l))
        app(app(rev1,0),nil) -> 0
        app(app(rev1,app(s,x)),nil) -> app(s,x)
        app(app(rev1,x),app(app(cons,y),l)) -> app(app(rev1,y),l)
        app(app(rev2,x),nil) -> nil
        app(app(rev2,x),app(app(cons,y),l)) -> app(rev,app(app(cons,x),app(app(rev2,y),l)))
        app(app(map,f),nil) -> nil
        app(app(map,f),app(app(cons,x),xs)) -> app(app(cons,app(f,x)),app(app(map,f),xs))
        app(app(filter,f),nil) -> nil
        app(app(filter,f),app(app(cons,x),xs)) -> app(app(app(app(filter2,app(f,x)),f),x),xs)
        app(app(app(app(filter2,true),f),x),xs) -> app(app(cons,x),app(app(filter,f),xs))
        app(app(app(app(filter2,false),f),x),xs) -> app(app(filter,f),xs)
        
)