Letters are tools for people to exchange feelings and deliver messages. The letters are nicknamed as follows. In ancient times before the invention of paper, the common "letters" were "wooden slips", also called "foot slips". Later, "letters" became a general term for letters.
The ancients also wrote it on silk books and then put it in the middle of something to send it, which is called "ruler" to refer to letters. Carp can also refer to letters. The classic comes from the poem "Yuefu" in the Han Dynasty: "Guests come from afar and leave me a pair of carp. Tell the boy to open the wooden box and write a letter with a ruler. " Hongyan handed me the book and it was published. Biographies of Su Wu: The son of heaven shot wild geese in the forest, and many silk books were written, saying that Wu and others were in a river. Since then, letters have often been replaced by "Hongyan".