Mitsunori Ogihara Alan’s friends and colleagues

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With great sadness, we report the passing of Alan L. Selman, who left this world on January 22, 2021. Alan was a long-time editor of the journal and served as Editor-in-Chief for eighteen years. Under Alan’s leadership, the journal Theory of Computing Systems grew significantly.

Alan received his Ph.D. in Mathematics in 1970 from the Pennsylvania State University. His advisor was Paul Axt, a student of Stephen Kleene. Following faculty appointments at the Pennsylvania State University, Iowa State University, and Northeastern University, he became the department chair of the Department of Computer Science (currently the Department of Computer Science and Engineering) at the University at Buffalo in 1990. He retired from the university in 2014.

Alan received various awards, including a Fulbright award, a Humboldt award, a Japan Society for the Promotion of Science (JSPS) award, and the Chancellor’s Award for Excellence in Scholarship and Creative Activities from the University at Buffalo. He was elected a Fellow of the Association for Computing Machinery (ACM) in 1998. He received the ACM-SIGACT Distinguished Service Prize to recognize his contribution to computational complexity, notably for co-founding the Conference on Computational Complexity (formerly known as Structure in Complexity Theory).

Alan’s research grew out of mathematical logic and recursion theory. His 1970 thesis classified sets of logical sentences that have finite models of specified cardinalities according to degrees of undecidability. To classify the sets of allowed cardinalities for models of first-order sentences, complexity theory lay waiting for Alan’s joint work with Neil Jones in STOC 1972: these sets comprise nondeterministic exponential time.

Alan was a leader in computational complexity. He introduced various important research topics, including p-selective sets, natural self-reducible sets, promise problems, reducing search to decision problems, comparison of resource-bounded reducibilities, and multivalued nondeterministic functions. Alan also had done pioneering work in many areas of computational complexity theory, including sparse sets, relativization, average-case complexity, hierarchy theorems, structures of complete sets, and complexity of multivalued functions. He also edited two volumes, Complexity Theory Retrospective and Complexity Theory Retrospective II with Lane Hemaspaandra and published with Steve Homer Computability and Complexity Theory.

Alan’s academic family is extensive. He was a terrific, inspiring leader of the Western New York theory community, whose past and current members include Jin-Yi Cai, Kannan Govindarajan, Roger He, Sanjay Jain, Lane Hemaspaandra, Russ Miller, Ken Regan, Jim Royer, Atri Rudra, Joel Seiferas, D. Sivakumar, and many others. His Ph.D. graduates at Buffalo were Pavan Aduri, Andrew Hughes, Ashish Naik, Dung Nguyen, Samik Sengupta, and Liyu Zhang. Alan brought several visitors to Buffalo, including Reuven Bar-Yehuda in 1992 and Christian Glaßer, Edith Hemaspaandra, and Mitsu Ogihara as postdocs. Alan, along with Bobby Kleinberg and Atri Rudra, organized a series of EaGL (Eastern Great Lakes) theory workshops (one of which was a Turing centennial). The workshop brought theoreticians from schools within a few hours of driving from Buffalo for a weekend workshop on theory of computation. Beyond the Western New York theory group (University at Buffalo, University of Rochester, and Rochester Institute of Technology), the workshop had drawn participants from Canada (University of Waterloo and University of Toronto) and USA (Carnegie Mellon University, Cornell University, Denison University, Oberlin College, Pennsylvania State University, and Syracuse University).

While being a scholar of uncanny vision and incredible ingenuity, Alan was a lovely human being. He was generous with his time for his students and colleagues, always willing to offer consultation and advice. He loved visual arts, music, and food, always impeccably dressed in his trademark flat cap. He traveled extensively around the world. Wherever he traveled, he was with his wife of more than 50 years, Dr. Sharon Selman. With Sharon by his side, Alan looked so happy and relaxed.

The field of theoretical computer science has lost a giant. Alan is no longer here to lead us, but his legacy will live on.