When the light is lit, the cab is empty and available; when it is not lit, the cab is unavailable.
When it is not lit, the cab is unavailable. When the light is lit, the cab is empty and available.
When the light is lit, the cab is empty and available. When it is not lit, the cab is unavailable.
When the light is lit, the cab is empty and available. When it is not lit, the cab is unavailable.