(VAR x y z )
(RULES 
        rev(nil) -> nil
        rev(.(x, y)) -> ++(rev(y), .(x, nil))
        car(.(x, y)) -> x
        cdr(.(x, y)) -> y
        null(nil) -> true
        null(.(x, y)) -> false
        ++(nil, y) -> y
        ++(.(x, y), z) -> .(x, ++(y, z))
        
)