Mark a book as incompatible with ACL2(p) waterfall parallelism.
Some features of ACL2 are incompatible with ACL2(p); see unsupported-waterfall-parallelism-features. For example, ACL2(p) does not
support clause-processors that modify the ACL2 state.
The form (non-parallel-book) instructs ACL2 to ensure that waterfall-parallelism is turned off. When you put that form into a book, it
will be ignored when including the book unless keyword :check-expansion
is true. (Suggestion: avoid that keyword unless you are sure you know what
you are doing!)