Gordon D. Plotkin. Some Varieties of Equational Logic. In Kokichi Futatsugi, Jean-Pierre Jouannaud, José Meseguer, editors, Algebra, Meaning, and Computation, Essays Dedicated to Joseph A. Goguen on the Occasion of His 65th Birthday. Volume 4060 of Lecture Notes in Computer Science, pages 150-156, Springer, 2006. [doi]
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