This book is one of its series of mathematical stories, which mainly includes four stories: the adventure of mathematical glasses, the battle in the castle, the adventure in the black forest and the adventure in the desert town. Professor Li Yupei is a famous popular science writer in China. He is very good at using children's favorite fairy tales and stories to make abstract and boring mathematics knowledge simple and interesting, so that readers can get in touch with mathematics in interesting stories and enjoy mathematics from now on. This book is one of his series of mathematical stories, which mainly includes two series of stories: Living Immortal, Zhuge Xiao and Erxiu.