Writing a book about C isn't the same thing as "write me a mail server in C". The right analogy here is you read their book about C and write another one in ex

Writing a book about C isn't the same thing as "write me a mail server in C". The right analogy here is you read their book about C and write another one in exactly (enough) style that your book can stand in for theirs, but you sell it for pennies.