(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)
)