Nineteen point trick play

Nineteen point trick play  

The extension at here is the famous nineteen point trick play (also known as the "eighteen and a half point trick play"). Typical continuations for this joseki would be at a or b: see 3-4 point low approach one-space low pincer press.

If White falls into this trick play, Black will give up nineteen points in the corner (hence the name "nineteen point trick play") but get a huge advantage anyway. Read on!

Nineteen point trick play  

and : she is taken in by this trick play.

Nineteen point trick play  

White happily captures the corner, blissfully unaware that Black is intending to sacrifice the corner.

Tas: Is w3 the best? It seems to me that a would remove a black liberty to avoid black getting b in sente later, And white b would threaten to break the wall.

Nineteen point trick play  

Possibly this?

Nineteen point trick play  

This seems even worse for white I think. Although the black wall is less perfect, white is running on the second line. Or am I missing something obvious?

Nineteen point trick play  

shmolex: what happens if white instead connects on the first line with 2? It seems like black doesn't get the wall anymore.

Nineteen point trick play ( at marked stone)  

The sequence up to results in a huge success for Black. White has 19 points in the corner, but Black has such a thick wall outside that its value is much bigger than White's corner. Besides, Black a is sente. (The Iron Wall page shows a continuation of this example.)

Nineteen point trick play counterplay  

White can play at to break this trick play. Black must defend at and attacks . The result is favourable for White. The three white stones around form a big bulge.

Nineteen point trick play counterplay  

Alternatively, White can choose to play at and in this diagram. The effect is similar.