Joseki of the week 3

This week, shusaku’s kosumi is highlighted.

White plays a low approach to blacks 4-3 stone and black responds with the high diagonal.

Black can gain a nice shape by extending along the top. White might like to prevent this with a play around a or b, but without support in the upper right of the board, it is easy to end up in trouble.

White needs to look after his stone at c15 to prevent black either playing a pincer or pressing down at a.
If white plays the two space extension, black protects the corner then exends to 4. White 1 is closer than ideal, so black can afford to strenghen white this way.
Instead of playing 2, black can now make the good extension at b. if white doesn’t extend up around c, black can press down on the two space extension and gain a wall facing b.

If white plays the 3 space extension instead, black immediatelly invades rather than protecting the corner first.
After the exchange, both players have thick shapes and white has an open skirt on the corner, however black has gained sente.

If there are any questions about the joseki of the week,
or if they are too basic, let us know in the comments!