Wang Yusheng, a mathematician in his 80s, remembers that, after he enrolled in the Graduate School of the Chinese Academy of Sciences in 1978, he would often spend half of his monthly allowance on collecting postage stamps, and sometimes wait outside post offices very early in the morning for newly issued stamps.

He was excited to share his interest in and lifelong commitment to both math and stamps at the launch ceremony of a collection of four themed stamps recently in Beijing.

He was joined by Gu Yunuo, a student in Shijiazhuang, Hebei province, who runs a social network account working out math problems. The two conducted a dialogue on why learning math matters.