Switching theory was developed as a theory for relay circuits in early days. In September 1935 Akira Nakashima of NEC delivered his invited speech on synthesis theory of relay networks including de Morgan’s theorem at the technical meeting of the Telegraph and Telephone Society in Tokyo. Since 1934 he had published his ideas in a series of papers “Theory and practice of relay circuits." Akira Nakashima and Masao Hanzawa formulated the design method for switching networks by using algebra in 1936. This is the first paper on switching theory that was applied to the analysis of digital circuits. It was in 1938 that the paper on switching theory was published by Claude E. Shannon. Following Nakashima’s research Kan-ichi Ohashi, Mochinori Goto and Yasuo Komamiya of Electrotechnical Laboratory (ETL) extended the theory to apply to sequential circuits.