(VAR X L X1 X2)
(RULES 
active(incr(nil)) -> mark(nil)
active(incr(cons(X,L))) -> mark(cons(s(X),incr(L)))
active(adx(nil)) -> mark(nil)
active(adx(cons(X,L))) -> mark(incr(cons(X,adx(L))))
active(nats) -> mark(adx(zeros))
active(zeros) -> mark(cons(0,zeros))
active(head(cons(X,L))) -> mark(X)
active(tail(cons(X,L))) -> mark(L)
mark(incr(X)) -> active(incr(mark(X)))
mark(nil) -> active(nil)
mark(cons(X1,X2)) -> active(cons(mark(X1),X2))
mark(s(X)) -> active(s(mark(X)))
mark(adx(X)) -> active(adx(mark(X)))
mark(nats) -> active(nats)
mark(zeros) -> active(zeros)
mark(0) -> active(0)
mark(head(X)) -> active(head(mark(X)))
mark(tail(X)) -> active(tail(mark(X)))
incr(mark(X)) -> incr(X)
incr(active(X)) -> incr(X)
cons(mark(X1),X2) -> cons(X1,X2)
cons(X1,mark(X2)) -> cons(X1,X2)
cons(active(X1),X2) -> cons(X1,X2)
cons(X1,active(X2)) -> cons(X1,X2)
s(mark(X)) -> s(X)
s(active(X)) -> s(X)
adx(mark(X)) -> adx(X)
adx(active(X)) -> adx(X)
head(mark(X)) -> head(X)
head(active(X)) -> head(X)
tail(mark(X)) -> tail(X)
tail(active(X)) -> tail(X)
)