Nie's poem "Anshun rushes to the ferry, and most of them rush to the bridge". What's the topic?

1979 10, Comrade Nie wrote an inscription for the Dadu River Memorial Hall, feeling the heroic spirit of the Red Army crossing the Dadu River and the main process of our army's victory in this battle, and wrote the following words: "Anshun seized the crossing, Dadu Bridge seized it, and the two armies were caught in the river, and Luding was in the next knowledge." It reflects the actual situation of our army crossing the Dadu River.