(VAR X Y X1 X2)
(RULES 
a__nats -> a__adx(a__zeros)
a__zeros -> cons(0,zeros)
a__incr(cons(X,Y)) -> cons(s(X),incr(Y))
a__adx(cons(X,Y)) -> a__incr(cons(X,adx(Y)))
a__hd(cons(X,Y)) -> mark(X)
a__tl(cons(X,Y)) -> mark(Y)
mark(nats) -> a__nats
mark(adx(X)) -> a__adx(mark(X))
mark(zeros) -> a__zeros
mark(incr(X)) -> a__incr(mark(X))
mark(hd(X)) -> a__hd(mark(X))
mark(tl(X)) -> a__tl(mark(X))
mark(cons(X1,X2)) -> cons(X1,X2)
mark(0) -> 0
mark(s(X)) -> s(X)
a__nats -> nats
a__adx(X) -> adx(X)
a__zeros -> zeros
a__incr(X) -> incr(X)
a__hd(X) -> hd(X)
a__tl(X) -> tl(X)
)