(VAR x y )
(RULES 
        int(0, 0) -> .(0, nil)
        int(0, s(y)) -> .(0, int(s(0), s(y)))
        int(s(x), 0) -> nil
        int(s(x), s(y)) -> int_list(int(x, y))
        int_list(nil) -> nil
        int_list(.(x, y)) -> .(s(x), int_list(y))
        
)