city distance

Hello all, I've been learning LUA for about a week now, and I think I have a handle on it, but I am unsure about making a LUA function. It will be an ability from a wonder that will increase a city's production on whatever it is currently constructing (whether a unit, building, wonder, etc.)...

I would like a lens that showed the number of cities within your civilization that are within 6 tiles Another lens that showed the number of cities within 9 tiles (for when you are suzerain of Toronto etc.) would be good too. Alternate lenses that show not just your cities but all cities within...