is a double atari. It reduces each of the marked black chains to one liberty. Black can only save one of his marked groups.
Failure to see a double atari can be very costly in games.
See the double atari coming! Get stronger overnight!
Here is too close; at a would be safer. But can you see the double atari yet?
Depends. Ready for a ko fight?
After White will collapse, unless the ko fight can be won.