(VAR X Y Z)
(RULES 
from(X) -> cons(X,n__from(s(X)))
sel(0,cons(X,Y)) -> X
sel(s(X),cons(Y,Z)) -> sel(X,activate(Z))
from(X) -> n__from(X)
activate(n__from(X)) -> from(X)
activate(X) -> X
)