A correction and a question about chapter1

[Novemgron]

1.4.3: A simple real-world example: parallel quicksort

In the end of this part, an example of 4-core computer is given. The ProcessCount should be 4 thus log2(4) in the expression.

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1.2: Start with terminology

Here is the example about the relationship of terms:

For example, concurrency is, by deinition, multithreading, but multithreading isn’t necessarily concurrent.

I think these words indicates that concurrency implies multithreading, whose inverse surely makes no sense. But when I read the part introducing multithreading(1.2.5 Multithreading for performance improvement), the declaration is:

Multithreading implies concurrency, but concurrency doesn’t necessarily imply multithreading.

The two propositions seem conflicting, which confused me a lot. If it is not a mistake, could you please help me understand it? I am really puzzled by the two statements. By the way, the figure1.8 in the end of 1.2 showing the relationship between the terms just introduced is confilct with the first statement, and not one-hundred-percent the same as the second statement.