to the international journal Journal of Combinatorial Theory, Series A. He wrote to its editorial board that he had essentially solved the problem, and the editors replied to him that if what he said was true, it would be a major achievement. (Many leaders in the field had worked on the problem starting from in 1917. Only a few special cases were solved at the time. A note published by in 1981 said: "[A]n extensive amount of work has been done on [this] problem ... This problem remains far from settled however".) So he brushed up his English and borrowed a typewriter to type up his work. It was a tremendous task for him as he could type at most four pages a night. He submitted a total of nearly 200 typed pages to the journal. The journal received six of his series of papers between September 1981 and March 1983 and published the first three in March 1983. The editors informed him that they would also publish his next three papers. He also sent a paper on resolvable balanced incomplete block designs to Acta Mathematica Sinica in August 1979, and a revised version was received by the journal in September 1983. This paper was published in July 1984 and was regarded as equally important by international experts. In spite of his heavy teaching duties, he carried on with his private mathematical research, often working until after midnight. He also made occasional trips to Beijing to find library resources. He told his colleagues that while he liked physics more, certain material conditions were required for physics research, but he only needed paper to do mathematics. Unfortunately, laborious work and harsh living conditions made his health deteriorate over time. His family of four lived in a small house of ten-odd square meters. The only table at home was used by his daughters, so he had to do his calculations on a broken kang bed-stove. On his trips to Beijing, he bought hard seat tickets since he could not afford sleeper tickets. He ate his dried food in a library in the daytime and slept on a bench in a train station at night. He sometimes wrote in his diary about how his mental fatigue affected his research and his teaching, and that he needed to get healthier for his research. After he had received dozens of copies of the journal issue