Help! My corkboard and outline have disappeared

There used to be a little notch by the title of my project in the binder, which I would click on to toggle the subchapters on and off. That notch has disappeared, and I am unable to view my corkboard and my outline. Does anyone know what might have caused this and how I can get it back? I don’t remember doing anything to remove it…? All I get is a blank corkboard and a blank outline screen when I switch.

Okay, I figured it out. Somehow my subchapters became individual files. Don’t know how that happened, but I moved them all back under the original binder heading, and now I have my corkboard and outline back!