The hang has been going on for over 24 hours. Photos won't let you quit the application without force quitting. Which I did a couple of times before seeing a post that I shouldn't do it.
I have another program called Power Photos from which I can access all my libraries. It shows which library is active in Photos and you can select another one for Photos to open. It shows the hanging one as the one open in Photos.
I can view individual photos in Power Photos and open them in Preview. Should I try to get Power Photos to open the problem library?