Mostly just the explanations of how the two cities could function as separate entities while physically occupying the same land through the use of legally manda

Mostly just the explanations of how the two cities could function as separate entities while physically occupying the same land through the use of legally mandated "useeing". The author goes into detail how this works -- obviously at one level people see the people, vehicles, etc. from the other city or they'd run into them, but on a conscious level they act as if they don't exist.