Bourbaki dangerous bend symbol
The dangerous bend or caution symbol ☡ (U+2621 ☡ CAUTION SIGN) was created by the Nicolas Bourbaki group of mathematicians and appears in the margins of mathematics books written by the group. It resembles a road sign that indicates a "dangerous bend" in the road ahead, and is used to mark passages tricky on a first reading or with an especially difficult argument.[1]
Certains passages sont destinés à prémunir le lecteur contre des erreurs graves, où il risquerait de tomber; ces passages sont signalés en marge par le signe ☡ (« tournant dangereux »)
Some passages are designed to forewarn the reader against serious errors, where he risks falling; these passages are indicated in the margin with the sign ☡ ("dangerous bend")
Nicolas Bourbaki's description of the symbol in several textbooks[2]
Variations[edit]
Others have used variations of the symbol in their books. The computer scientist Donald Knuth introduced an American-style road sign depiction in his Metafont and TeX systems, with a pair of adjacent signs indicating doubly dangerous passages.[3][4][5][6]
Typography[edit]
In the LaTeX typesetting system, Knuth's dangerous bend symbol can be produced by
first loading the font manfnt (a font with extra symbols used in Knuth's TeX manual) with
\usepackage{manfnt} and then typing \dbend
There are several variations given by \lhdbend, \reversedvideodbend, \textdbend, \textlhdbend, and \textreversedvideodbend.
In popular culture[edit]
The Twenty One Pilots song, "Overcompensate", makes direct reference to the symbol. Since 2018, the Nicolas Bourbaki group has also been referenced in the conceptual narrative of the band.[7][8]
See also[edit]
References[edit]
- ^ Steven G. Krantz (2011), The Proof Is in the Pudding: The Changing Nature of Mathematical Proof, Springer, ISBN 0-387-48908-8, p. 92.
- ^ See, for example, Théorie des ensembles, p. I-8.
- ^ Donald Ervin Knuth (1986), The METAFONTbook, Addison-Wesley, ISBN 0-201-13445-4.
- ^ Donald Ervin Knuth (1984), The TeXbook, Addison-Wesley, ISBN 0-201-13448-9.
- ^ George J. Tourlakis (2003), Lectures in Logic and Set Theory, Volume 2: Set Theory, Cambridge University Press, ISBN 0-521-75374-0, p. xiv.
- ^ Gerard P. Michon (2012), Dangerous Bend Symbol, doubled and tripled, Numericana.
- ^ Kaufman, Gil (February 29, 2024). "Twenty One Pilots Announce 'Clancy' Album, Drop Video For Booming 'Overcompensate' Single". Billboard. Retrieved March 1, 2024.
- ^ "Map of Dema". dmaorg.info. Retrieved October 7, 2018.
External links[edit]
- Knuth's use of the dangerous bend sign. Public domain GIF files.
- Latex style file to provide a "danger" environment marked by a dangerous bend sign, based on Knuth's book.
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