(VAR X Y Z X1 X2)
(RULES 
a__2nd(cons(X,cons(Y,Z))) -> mark(Y)
a__from(X) -> cons(mark(X),from(s(X)))
mark(2nd(X)) -> a__2nd(mark(X))
mark(from(X)) -> a__from(mark(X))
mark(cons(X1,X2)) -> cons(mark(X1),X2)
mark(s(X)) -> s(mark(X))
a__2nd(X) -> 2nd(X)
a__from(X) -> from(X)
)