"If Black omits the defensive move and attacks prematurely at 4...."
There are two 's in the diagram (D5 and F4 if you look at the code for the diagram). Perhaps the at D5 should be an empty point? If not, White has an extra stone, so F4 should become an empty point.
![[Welcome to Sensei's Library!]](images/stone-hello.png "Sensei's Library")
![[Diagram]](diagrams/22/8e0212a4d8595402621f7aa5a8debf06.png)
's in the diagram (D5 and F4 if you look at the code for the diagram). Perhaps the