What are the limitations on the One City achievement?  I read that its OK to Culture-flip a city, but is it OK to take a city through war?  Is it OK to take a Settler unit from another civ. and build a city? Or would this negate the achievement?  I read that if you Culture-flip a city you cannot build anything in that city? Is that true? That city is relegated to science or gold production only? I play on the iPad, Achievements are not supported, but am interested in knocking them out anyway.