(2) "Creating Characters in Cangjie" tells us that when there were no characters, the ancients exchanged ideas by knotting notes and stories. It is said that Cang Xie created Chinese characters by imitating the footprints of birds.
(3) The origin of books, classics and deletions tells us that characters were originally carved on flat things such as animal bones and tortoise shells, and for a long time in the middle, they were carved on objects such as bamboo and wood, and finally they were written on paper.