page_title: Bourbaki dangerous bend symbol
hierarchical_section_title: Bourbaki dangerous bend symbol
caption_attribution_description: Borne Michelin antérieure à 1949 d'annonce de succession de virages (France)
context_page_description: The dangerous bend or caution symbol ☡ 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.
  Others have used variations of the symbol in their textbooks, and 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.
context_section_description: 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.
  Others have used variations of the symbol in their textbooks, and 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.
caption: French "virages dangereux" road sign, before 1949
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