(VAR N X X1 X2 XS )
(RULES 
        a__from(X) -> cons(mark(X), from(s(X)))
        a__head(cons(X, XS)) -> mark(X)
        a__2nd(cons(X, XS)) -> a__head(mark(XS))
        a__take(0, XS) -> nil
        a__take(s(N), cons(X, XS)) -> cons(mark(X), take(N, XS))
        a__sel(0, cons(X, XS)) -> mark(X)
        a__sel(s(N), cons(X, XS)) -> a__sel(mark(N), mark(XS))
        mark(from(X)) -> a__from(mark(X))
        mark(head(X)) -> a__head(mark(X))
        mark(2nd(X)) -> a__2nd(mark(X))
        mark(take(X1, X2)) -> a__take(mark(X1), mark(X2))
        mark(sel(X1, X2)) -> a__sel(mark(X1), mark(X2))
        mark(cons(X1, X2)) -> cons(mark(X1), X2)
        mark(s(X)) -> s(mark(X))
        mark(0) -> 0
        mark(nil) -> nil
        a__from(X) -> from(X)
        a__head(X) -> head(X)
        a__2nd(X) -> 2nd(X)
        a__take(X1, X2) -> take(X1, X2)
        a__sel(X1, X2) -> sel(X1, X2)
        
)