(VAR fun x xs y )
(RULES 
        app(app(minus,x),0) -> x
        app(app(minus,app(s,x)),app(s,y)) -> app(app(minus,x),y)
        app(f,0) -> app(s,0)
        app(f,app(s,x)) -> app(app(minus,app(s,x)),app(g,app(f,x)))
        app(g,0) -> 0
        app(g,app(s,x)) -> app(app(minus,app(s,x)),app(f,app(g,x)))
        app(app(map,fun),nil) -> nil
        app(app(map,fun),app(app(cons,x),xs)) -> app(app(cons,app(fun,x)),app(app(map,fun),xs))
        app(app(filter,fun),nil) -> nil
        app(app(filter,fun),app(app(cons,x),xs)) -> app(app(app(app(filter2,app(fun,x)),fun),x),xs)
        app(app(app(app(filter2,true),fun),x),xs) -> app(app(cons,x),app(app(filter,fun),xs))
        app(app(app(app(filter2,false),fun),x),xs) -> app(app(filter,fun),xs)
        
)