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In some books I've seen this symbol $\dagger$, next to some theorem's name, and I don't know what it means. I've googled it with no results which makes me suspect it's not standard.

Does anybody know what it means? One example I'm looking at right now is in a probability book, next to a section about Sitrling's approximation to factorials:

Stirling's formula ($\dagger$)

FOUND IT: The preamble says they're historic notes, it actually makes a historic introduction in the section about Stirling's formula, inc ase anyone's wondering.

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    $\begingroup$ $\dagger$ is often a footnote symbol. Can it be there too? $\endgroup$ – Daniel Fischer Aug 23 '13 at 19:45
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    $\begingroup$ It is like a sword and maybe it means if you don't understand a notation, you'll lost your head. :-) $\endgroup$ – mrs Aug 23 '13 at 19:48
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    $\begingroup$ Could you either supply an image showing its usage, or reference to the text? Also note, books may have a guide to notation in the preamble, which may help you solve this mystery. Some textbooks use marks like this to indicate theorems of great importance. $\endgroup$ – Douglas S. Stones Aug 23 '13 at 19:51
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    $\begingroup$ The book's introduction may contain a statement such as "Some sections are instructive but outside the scope of the main topic, and can be skipped on a first reading. These sections are marked with a dagger symbol ($\dagger$)" or "This book can be used as the text for a one- or a two-semester course. For a one-semester course, omit the sections marked with a dagger ($\dagger$)." You should look in the book's introduction for such an explanation. $\endgroup$ – MJD Aug 23 '13 at 19:56
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    $\begingroup$ Also way off context, but Wikipedia says that $A^\dagger$ is the transpose of the complex conjugate of $A$. :) $\endgroup$ – apnorton Aug 23 '13 at 20:03
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From Wikipedia: "While the asterisk (asteriscus) was used for corrective additions, the obelus was used for corrective deletions of invalid reconstructions".

The obelus, which is the "cross", is similar to the asterisk but is used for making corrections instead of additions.

Edit: I don't know if this would necessarily be the correct context without further information (of what follows the cross).

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    $\begingroup$ That seems quite unlikely to be the case here, given the context. $\endgroup$ – Tobias Kildetoft Aug 23 '13 at 19:53
  • $\begingroup$ The other possibility is that it is used as a reconstruction of the formula from somewhere else. But I don't know if I am correct without further information. $\endgroup$ – Don Larynx Aug 23 '13 at 19:55
  • $\begingroup$ I don't think it's called an obelus, this is an obelus ÷. It's called a dagger, or sometimes obelisk en.wikipedia.org/wiki/Dagger_%28typography%29 $\endgroup$ – Celeritas Nov 3 '13 at 10:39
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It is often simply used as an alternative to an asterisk, or a footnote notation.

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    $\begingroup$ There is no footnote. I hope it's not the irrelevant information of the person being dead, because I'm now seeing a "Gauss ($\dagger$)" $\endgroup$ – MyUserIsThis Aug 23 '13 at 19:48
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    $\begingroup$ @MyUserIsThis It means Gauss was a saint. $\endgroup$ – L. F. Aug 23 '13 at 19:51
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It depends on the author choice. Some books are using it to show the kind of a specific problem (Harder, Article related, etc.) Some Books are using it to mark some chapters/sections as an independent one (or in your book as a historical section) you should refer to the book's preface to know the author mean. (Generally -old fashioned- it's a brother of asterisk on footnotes such as $\dagger$ double dragger instead of $*$,$**$,...)

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