Sealing in by cutting across

Starting position  

Black can set up a useful sequence by cutting across

Sealing in  

Black threatens to cut White apart. By capturing firmly with White keeps her stones connected, but now Black can play in sente, sealing White in.

On /discussion, we discuss the merits of giving atari by at a before capturing at .

Technique as explained by Tesuji Dictionary

From Fujisawa Hideyuki's Tesuji Dictionary (vol. I, p.63)  

In professional practice

Moves 45 to 51  

Black is O Meien, White is Lee Sedol. White is sealed in and proceeds at a to make life for his stones. resists against the above mentioned technique:

Moves 45 to 51  

Regardless the fact that makes a ladder that doesn't work, Black connecting with and is probably unbearable.