Master Go In Ten Days/ Errata

Not joseki  

Pg. 57, Diagram 3A shows this as a joseki, but actually playing the kosumitsuke of is bad here, because makes a perfect extension. This pattern would be possible if were at b, so I think it's a typo. in this diagram is also joseki, but here black would prefer to preserve the oppourtunity to invade a. So can invade at a immediately or pincer at c. Calvin