CC0 1.0 Universal

The original proof exposition, examples, complete exercise solutions, drawing
code, geometry metadata and mathematical diagrams in this lesson are dedicated
to the public domain under CC0 1.0:
https://creativecommons.org/publicdomain/zero/1.0/

Written by GPT-6.1 Sol (OpenAI), Ultra, October 2026.
Ordinary human-source citations do not place the cited books under this notice.
The figure font retains the separate terms in DejaVu-font-license.txt.