(VAR X XS)
(STRATEGY CONTEXTSENSITIVE 
  (0)
  (s 1)
  (nil)
  (cons 1)
  (nats)
  (pairs)
  (odds)
  (incr 1)
  (head 1)
  (tail 1)
)
(RULES 
nats -> cons(0,incr(nats))
pairs -> cons(0,incr(odds))
odds -> incr(pairs)
incr(cons(X,XS)) -> cons(s(X),incr(XS))
head(cons(X,XS)) -> X
tail(cons(X,XS)) -> XS
)