Zi Collection, Upper Volume, Page 12, Entry 03
The ancient form of the character "dan" is recorded in the "Shuowen Jiezi" (Shuowen Jiezi). Detailed annotations can be found in the "Radical: Dot (diǎn)" section, under the third stroke. The "Zihui" (Zihui) incorrectly rendered it as a different character form, which was an error and has now been corrected.