Thank you to the New York Post and to Greg Pollowitz for bringing attention to this Department of Homeland Security video, which suggests that if an active shooter comes into your building, you should evacuate, or hide, or at the very most try to fight back with scissors. You should definitely not help anyone who is injured, and you certainly shouldn’t have a gun.
https://youtube.com/watch?v=oI5EoWBRYmo
The video rather reminded me of this, from Blackadder Goes Forth:
Lieutenant George: Oh, sir, if we should happen to tread on a mine, what do we do?
Captain Blackadder: Well, normal procedure, Lieutenant, is to jump up 200 feet into the air and scatter yourself over a wide area.
Carry on.