How is there 'no node that c-commands B that A also c-commands'?

Question

_{Source: p 130, Syntax, A Generative Introduction (3 ed, 2012) by Andrew Carnie}

In this tree, A governs B. It c-commands B, and
[1.] there is no node that c-commands B that A also c-commands. [End of 1.]
(You should note that A also governs N under this definition, A c-commands N, and
there is no node that N c-commands that also c-commands A.
The reverse is also true: N governs A because the relationship between A and N is symmetric c-command. B does not govern A, because B does not c-command A.)

How is 1 true? Why is not N this node? A c-commands N, and N c-commands B.

Answer 1

As already in other questions you had, I would recommend you just having a look at the definition again:

X c-commands Y if X's sister either
a) is Y or
b) contains Y.

This means that nodes can only c-command their sisters and "nieces" (i.e. the daughters of their sisters, and daughters af these nieces and so on), NEVER their own daughters or "granddaughters", i.e. never something that they immediately or indirectly dominate.

Clearly, in this example, N and B don't satisfy the definition of c-command: B is neither a sister of N nor is it contained in a sister of N, but it is immediately dominated by N. So why do you think N c-commands B? This can NEVER be the case if N is the mother or "grandmother", "great-gramdmother"... of B, so there is no reason why N and B should stand in a c-command relation by this definition.