Double carp in ancient poetry?

Double carp is an allusion in ancient poetry, which comes from the folk song "Drinking Horses in Great Wall Cave" in Han Yuefu.

Drinking horses in the Great Wall Grottoes and Travel in Han Yuefu Folk Songs

Jiang Chun grass green, endless extension to the distance, makes me miss my husband who travels far away.

A husband who is far away from home can not miss him all day, but he can see him in his dream soon.

I saw him by my side in my dream and woke up to find that he was still in exile.

Different counties in different places, the exhibition will not meet.

Mulberry withered until the wind came, and the sea knew the taste of cold.

Fellow travelers home, dear, who will tell me the news of my husband?

A guest came from far away and brought me a carp-shaped wooden box with silk and silk letters in it.

Tell the boy to open the wooden box and write a letter with a ruler.

Kneeling for a long time to read a plain book, what is it like in the book?

The first part of the letter is to increase appetite. It is said that the second half of the letter is often left out.