in <PMake — A Tutorial>3.2. Including Other Makefiles:

PMake allows you to do the same thing for makefiles, with the added ability to use variables in the filenames. An include directive in a makefile looks either like this:

#include <file>
or this:

#include "file"

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while man page of make writes:

All such structures are
     identified by a line beginning with a single dot (‘.’) character.  Files
     are included with either .include ⟨file⟩ or .include "file".

I think the pmake book should change to ".include".