Bourbaki dangerous bend symbol
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. Variations. 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. Typography. 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 and then typing There are several variations given by codice_1, codice_2, codice_3, codice_4, and codice_5.