The allusion of double carp originated from the poem "Drinking Horses in the Great Wall Cave" written by Han Yuefu: "Guests come from afar, leave me with double carp and call for cooking carp. There is a ruler book in it. ? Kneeling for a long time to read a plain book, what is it like in the book? Words add vegetables, words look back. " In ancient times, people often used carp-shaped letters to cover books and letters, so many literati also used carp to refer to letters in their poems. Of course, cooking fish in the poem is not really cooking, but letting their son open a carp-shaped wooden box with a size.