On the bank of Fenggan Bridge outside the Imperial Palace, there is a stone tablet called "A line of water flows west here". It was built to commemorate the famous astronomers in the Tang Dynasty who came here to study arithmetic. "The trip here is a water flowing west" is an allusion, and the answer to this allusion should start with thich nhat hanh's identity.

Thich nhat hanh was a monk in the Tang Dynasty. Sui, Hebei Julu, Zhang Zhisun. During the kaiyuan period (7 13-74 1), Emperor Xuanzong of the Tang Dynasty forced him to come to Chang 'an, put him in the temple, and wrote books such as Photographing, Adjusting and Hiding, Records of the Stone, The Great Calendar of Kaiyuan, and The Great Sun Classic. After his death, posthumous title was greatly pitied.

He is the ancestor of China tantric school, astronomer, astronomer. 72 1, a group went to the National Assembly Temple in Tiantai Mountain. Why did he go to the imperial palace? In the 9th year of Kaiyuan (72 1), because the old calendar could not predict the solar eclipse, Emperor Xuanzong of the Tang Dynasty ordered thich nhat hanh to compile a new calendar. On the basis of comparing various calendars, the group put forward a new scheme.

During the compilation, I encountered some problems in astronomy and mathematics. He asked questions everywhere, but he always got nothing. Later, I learned that there was a great master who was proficient in mathematics in Xiaoguo Temple, so I came to Wan Li to find a teacher. This day, after days of heavy rain. Master Dazhen was sorting out calculations with the monks in the temple when he suddenly said, "It's time for a disciple to come and calculate today."

After a long time, the master said to himself, "The water in front of the door is flowing west, and it's time for a distant guest to arrive." The disciples were all surprised. "Kyoto to thich nhat hanh?" A loud announcement interrupted the whispering of the disciples. The earthquake immediately led the monks out of the city gate and greeted the party at Fenggan Bridge. In an instant, with a bang, the water under the bridge rolled to the west uncharacteristically.

This uncharacteristic landscape is one of the eight scenic spots on the rooftop, and it is the spectacle of "Double Flows Returning to Lan". So what's so strange about this landscape? The so-called Shuangliu refers to the northbound stream originating from Beishan in Tiantai and the westbound stream originating from the yellow mud at Lingzhi Peak. Two streams meet at Fenggan Bridge outside the temple, flow eastward and enter Zhexi. Beijian River flows down from Beishan Mountain and winds for dozens of miles, starting from National Day. Xijiang River flows down from Lingzhi Peak, but the process is only two or three miles.