《新唐书》里有篇《李密传》，
风趣的故事有一段，
说的是隋末辽东有一人，
名叫李密很能干。
他年轻时在皇室做侍卫，
办事情机智又果敢。
想不到隋炀帝说他不老实，
下旨把他的差事免。
李密一点也不懊丧，
回家发奋把书念。
一次李密骑牛出门去，
把一部《汉书》挂在牛角边，
一边赶路一边读，
被宰相杨素巧遇见。
杨素心中暗称奇，
坐车慢慢跟后边，
问清了读书少年是李密，
走近亲切把话谈，
看出了李密不是平庸辈，
回家后唤来儿子杨玄感，
告诉他李密的才气与学识，
要儿子经常去找李密玩。
从那后两个少年成好友，
砥行砺志把学问钻。
到后来觉察隋朝已腐败，
及时起兵把隋反。
杨玄感拜了李密做军师，
李密帮他出谋划策夺江山。
谁想关键时玄感未从李密计，
兵败身亡后果惨。
李密无处把身存，
投靠了瓦岗寨义军仍造反。
到后来当上一名大首领，
燃得那农民起义火燎原，
沉重地打击了统治者，
英名代代往后传。
“牛角挂书”这成语，
比喻人勤奋读书肯钻研。
Hang a Book on a Cow's Horn
In the“New History of Tang Dynasty”there was a biography of Li Mi。It was a very interesting story。It said that a man in the last reign of Sui Dynasty（581—618A。D。）in Liaodong Peninsular，by the name of Li Mi who was quite able。As a young man he served as a bodyguard in the court，where he proved to be witty and brave。But unfortunately Emperor Yang of Sui said he was dishonest，and ordered an end to his post。Young Li Mi，however，was not discouraged，and indulged in reading when he was back home。
One day，Li Mi went out of his village on cowback，hanging the“History of Han”on the horn of the cow。He was reading while travelling。It happened the prime minister Yang Su caught sight of this。Yang Su was amazed at the young lad，and followed him slowly in his imperial wagon。He was told that the lad's name was Li Mi，and approached him to talk to him。He found out Li Mi was not a nobody，and hurried home to call up his son Yang Xuangan。He told his son that Li Mi was talented and knowledge-able，and asked his son to frequent his place。
Later on the two young men became good friends and together they established and whetted their conducts and studies endlessly。Later on they found the Sui Dynasty tended to decay，so they organized an army and rose up against it without delay。
Yang Xuangan made Li Mi his military consultant，and Li Mi helped Yang Xuangan decide strategy to fight for the country。But in a key battle he didn't follow Li Mi's idea，and Xuangan got killed and his men all defeated。
Li Mi had nowhere to dwell，and had to join the Wagang village volunteers to rebel。Later he became a chief commander of a peasants uprising force，which heavily tore the foundation of the imperial rulers，and his heroism goes down from generation to generation。
You can use“Hang a Book on a Cow's Horn”as an idiom to praise a person who studies very hard。
