(VAR X Y X1 X2) (RULES active(nats) -> mark(adx(zeros)) active(zeros) -> mark(cons(0,zeros)) active(incr(cons(X,Y))) -> mark(cons(s(X),incr(Y))) active(adx(cons(X,Y))) -> mark(incr(cons(X,adx(Y)))) active(hd(cons(X,Y))) -> mark(X) active(tl(cons(X,Y))) -> mark(Y) active(adx(X)) -> adx(active(X)) active(incr(X)) -> incr(active(X)) active(hd(X)) -> hd(active(X)) active(tl(X)) -> tl(active(X)) adx(mark(X)) -> mark(adx(X)) incr(mark(X)) -> mark(incr(X)) hd(mark(X)) -> mark(hd(X)) tl(mark(X)) -> mark(tl(X)) proper(nats) -> ok(nats) proper(adx(X)) -> adx(proper(X)) proper(zeros) -> ok(zeros) proper(cons(X1,X2)) -> cons(proper(X1),proper(X2)) proper(0) -> ok(0) proper(incr(X)) -> incr(proper(X)) proper(s(X)) -> s(proper(X)) proper(hd(X)) -> hd(proper(X)) proper(tl(X)) -> tl(proper(X)) adx(ok(X)) -> ok(adx(X)) cons(ok(X1),ok(X2)) -> ok(cons(X1,X2)) incr(ok(X)) -> ok(incr(X)) s(ok(X)) -> ok(s(X)) hd(ok(X)) -> ok(hd(X)) tl(ok(X)) -> ok(tl(X)) top(mark(X)) -> top(proper(X)) top(ok(X)) -> top(active(X)) )