(VAR N X X1 X2 Y Z )
(RULES 
        terms(N) -> cons(recip(sqr(N)), n__terms(s(N)))
        sqr(0) -> 0
        sqr(s(X)) -> s(add(sqr(X), dbl(X)))
        dbl(0) -> 0
        dbl(s(X)) -> s(s(dbl(X)))
        add(0, X) -> X
        add(s(X), Y) -> s(add(X, Y))
        first(0, X) -> nil
        first(s(X), cons(Y, Z)) -> cons(Y, n__first(X, activate(Z)))
        terms(X) -> n__terms(X)
        first(X1, X2) -> n__first(X1, X2)
        activate(n__terms(X)) -> terms(X)
        activate(n__first(X1, X2)) -> first(X1, X2)
        activate(X) -> X
        
)