But other citizens don't have to prove they will be in a city in the future to prove residency; it's sufficient to prove they've been in a city in the past to f

But other citizens don't have to prove they will be in a city in the future to prove residency; it's sufficient to prove they've been in a city in the past to fulfill residency requirements. I can move to a town, register to vote after the residency requirement is fulfilled, move away the very same day, and still vote in that city until I have residency elsewhere. Why should it work any differently for a homeless person?