You’re the new doorman for your apartment. You unlock and lock the door for people who want to come in. They come up to your window, show you their ID and Entry Request paper, and you check it. If everything looks good, including their appearance, you unlock the door for them. If something is wrong, they’re a doppelgänger and you need to call the D.D.D who will come and take care of it. Doppelgängers are dangerous monsters and you need to keep your neighbors safe.