(VAR X N L X1 X2)
(RULES 
active(zeros) -> mark(cons(0,zeros))
active(and(tt,X)) -> mark(X)
active(length(nil)) -> mark(0)
active(length(cons(N,L))) -> mark(s(length(L)))
active(cons(X1,X2)) -> cons(active(X1),X2)
active(and(X1,X2)) -> and(active(X1),X2)
active(length(X)) -> length(active(X))
active(s(X)) -> s(active(X))
cons(mark(X1),X2) -> mark(cons(X1,X2))
and(mark(X1),X2) -> mark(and(X1,X2))
length(mark(X)) -> mark(length(X))
s(mark(X)) -> mark(s(X))
proper(zeros) -> ok(zeros)
proper(cons(X1,X2)) -> cons(proper(X1),proper(X2))
proper(0) -> ok(0)
proper(and(X1,X2)) -> and(proper(X1),proper(X2))
proper(tt) -> ok(tt)
proper(length(X)) -> length(proper(X))
proper(nil) -> ok(nil)
proper(s(X)) -> s(proper(X))
cons(ok(X1),ok(X2)) -> ok(cons(X1,X2))
and(ok(X1),ok(X2)) -> ok(and(X1,X2))
length(ok(X)) -> ok(length(X))
s(ok(X)) -> ok(s(X))
top(mark(X)) -> top(proper(X))
top(ok(X)) -> top(active(X))
)