(VAR X XS )
(RULES 
        nats -> cons(0, n__incr(nats))
        pairs -> cons(0, n__incr(odds))
        odds -> incr(pairs)
        incr(cons(X, XS)) -> cons(s(X), n__incr(activate(XS)))
        head(cons(X, XS)) -> X
        tail(cons(X, XS)) -> activate(XS)
        incr(X) -> n__incr(X)
        activate(n__incr(X)) -> incr(X)
        activate(X) -> X
        
)