A calculus for four-valued sequential logic.

Jan A. Bergstra Jaco van de Pol A calculus for four-valued sequential logic. 3122-3128 2011 412 Theor. Comput. Sci. 28 https://doi.org/10.1016/j.tcs.2011.02.035 https://www.wikidata.org/entity/Q62047456 db/journals/tcs/tcs412.html#BergstraP11