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  *  
    (Top)
  *  
    1Variations
  *  
    2Typography
  *  
    3See also
  *  
    4References
  *  
    5External links

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Bourbaki dangerous bend symbol

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From Wikipedia, the free encyclopedia
Typological symbol representing difficulty
[220px-Borne_Michelin_Virages]French "virages dangereux" road sign,
before 1949

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 destines a premunir le lecteur contre des
    erreurs graves, ou il risquerait de tomber ; ces passages sont
    signales 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]

[60px-Kn]Knuth's "Dangerous Bend" sign

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.

See also[edit]

  * Halmos box

References[edit]

 1. ^ Steven G. Krantz (2011), The Proof Is in the Pudding: The
    Changing Nature of Mathematical Proof, Springer, ISBN 
    0-387-48908-8, p. 92.
 2. ^ See, for example, Theorie des ensembles, p. I-8.
 3. ^ Donald Ervin Knuth (1986), The METAFONTbook, Addison-Wesley, 
    ISBN 0-201-13445-4.
 4. ^ Donald Ervin Knuth (1984), The TeXbook, Addison-Wesley, ISBN 
    0-201-13448-9.
 5. ^ George J. Tourlakis (2003), Lectures in Logic and Set Theory,
    Volume 2: Set Theory, Cambridge University Press, ISBN 
    0-521-75374-0, p. xiv.
 6. ^ Gerard P. Michon (2012), Dangerous Bend Symbol, doubled and
    tripled, Numericana.

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.

*
Retrieved from "https://en.wikipedia.org/w/index.php?title=
Bourbaki_dangerous_bend_symbol&oldid=1057427872"
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  * Nicolas Bourbaki

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  * This page was last edited on 27 November 2021, at 15:53 (UTC).
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