(VAR N X Y )
(RULES 
        terms(N) -> cons(recip(sqr(N)))
        sqr(0) -> 0
        sqr(s) -> s
        dbl(0) -> 0
        dbl(s) -> s
        add(0, X) -> X
        add(s, Y) -> s
        first(0, X) -> nil
        first(s, cons(Y)) -> cons(Y)
        
)