Following the Tang Dynasty (618-907) poetry, ci, a kind of classical Chinese poetry, of the Song Dynasty (960-1279) marked a new pinnacle in Chinese literary history. Huanxisha, a representative work by the renowned poet Yan Shu, expresses the sentiment about spring time, containing the reflection of life. The whole poem reiterates the same topic by clinging to the new and the old, the gone and the coming, and the changing and the unchanging. The weather, the pool, the pavilion and the sunset do not change, but today's returning swallows are possibly not those last year. In the circulation and repetition, some alternation of the new and the old unnoticeably takes place, which makes the adopted persona feel melancholy. The two lines starting with "helplessly" regret the past with the first line, and greet the new with the second. They contain a little subtle sentiment within joyance, full of poetry and speculation, and are thus famous lines which have been recited through generations.