I'm a bit confused as to how amenities and luxury resources work. I know one luxury resource can provide something like 4 amenity (1 to each city). If I have 2 of the same luxury resource and 8 cities, does each city then automaticlaly have 1 amenity? If I trade the resource do 4 of the cities go down 1 amenity? The city details screen doesn't tell me which luxury resource is providing the amenity and I'd like to have some more information so I can trade.