Dropping back with a diagonal play

Dropping back one line  

This is from a game Nie Weiping-Ma Xiaochun (B) 1990-09-02.

Black has a problem with many cutting points here.

If Black plays at one of a or b, and White at the other, Black will block but have two cutting points.

The idea of is to reduce the number by one ^[1], compared to playing at a or b. It is a bargain to do this at a cost only of one point of territory when White later plays at a.

Charles Matthews

Strike at the waist  

By the way, something more to say here: White would actually think more about cutting this way, across the knight's move (marked stones). But now Black can answer not just at a (when White can create two cutting points), but at b or c.

Continuation  

Black's shape here is reasonable.