 | Problems have been found in this book. (rev 331971603, at 06:13 16 December 2009 (UTC)). For a detailed explanation of the problems found, and on how to fix them, click on [show] at the right of the blue lines. Duplicate articles Duplicate articles are articles that are included more than once. These are usually the result of redirects to the same article, and unintentional. Although this should not happen very often, it is possible that some articles are intentionally duplicated. Mark these with a comment below the link, such as: :[[Hydrogen]] <!--This article is intentionally included twice in the book because ... -->Comments on the same line as the link will cause the article to be ignored by the PDF.
:[[Hydrogen]] <!--This article is intentionally included twice in the book because ... -->
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