I messed up my groups display...

A window got a few keystrokes sent to it unintentionally, and now
my groups display has some kind of foldable tree display of
entries like

[ Gnus -- 126863 ]
3:    3481 /  834! 38234: nnimap+myserver:user.bob.events.atlanta
3:    1105 /  212! 13342: nnimap+myserver:user.bob.events.newhampshire
  [ misc -- 62446 ]
1:    3189 /     ! 14943: nndraft:drafts
3:         /   18!   284: nndoc+/home/bob/deal-really:deal-really
3:      18 /  1059! 128714: nnimap+myserver:INBOX


What did I invoke? How do I make it go away?

And if I use kill and yank to reorder the buffer, is there a way to
save and restore multiple orderings?

  --thanks for any clues...
  --a