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The third floor of the warehouse on West 45th Street in Manhattan was a sprawl of rotting wood when the two artists first arrived.

Yet through the windows came north light, softened and diffused. The newlywed couple envisioned their future studios and moved in.

They put down bamboo floors, erected walls, built a kitchen and bathroom and raised two daughters in a home they have loved for over four decades.

Then a new set of digital locks that rely on a smartphone app arrived.

Now, the couple — Mary Beth McKenzie, 72, and Tony Mysak, 93 — find themselves waging a legal battle over access to their home that has raised an analog question: Do renters have the right to an old-school metal key?