Bourbaki dangerous bend symbol

The dangerous bend symbol was created by Nicolas Bourbaki and appears in the margins of mathematics books written by the group. It is analogous with a street sign that indicates a "dangerous bend" in the road ahead. Bourbaki, and those who later adopted the symbol, would use it to mark passages that were tricky on a first reading or contained an especially difficult argument. For example, computer scientist Donald Knuth uses it in his textbooks.

References

File:Rkinch db.gif

Knuth's "Dangerous Bend" sign.

• Knuth's use of the dangerous bend sign. Public domain GIF files.

See also

• Halmos box