Barnaby Martin, Jos Martin. The Complexity of Positive First-Order Logic without Equality II: The Four-Element Case. In Anuj Dawar, Helmut Veith, editors, Computer Science Logic, 24th International Workshop, CSL 2010, 19th Annual Conference of the EACSL, Brno, Czech Republic, August 23-27, 2010. Proceedings. Volume 6247 of Lecture Notes in Computer Science, pages 426-438, Springer, 2010. [doi]
Abstract is missing.