The "Three Constantly Read Articles" (老三篇, lao san pian) were early political essays written by Mao Zedong before 1949. They were entitled In Memory of Norman Bethune, dedicated to Norman Bethune; Serve the People, written in memory of Zhang Side; and Yu Gong, The Foolish Old Man Who Removed the Mountains - represented on this poster by Chen Yonggui.
Below the image are the text and notation and lyrics of the song "Study the Three Old Articles Forever" (永远学习‘老三篇’).