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.