(VAR f 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(double,0) -> 0
        app(double,app(s,x)) -> app(s,app(s,app(double,x)))
        app(app(plus,0),y) -> y
        app(app(plus,app(s,x)),y) -> app(s,app(app(plus,x),y))
        app(app(plus,app(s,x)),y) -> app(app(plus,x),app(s,y))
        app(app(plus,app(s,x)),y) -> app(s,app(app(plus,app(app(minus,x),y)),app(double,y)))
        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)
        
)