Classical mereology is not elementarily axiomatizable

@article{Pietruszczak2015ClassicalMI,
  title={Classical mereology is not elementarily axiomatizable},
  author={A. Pietruszczak},
  journal={Logic and Logical Philosophy},
  year={2015},
  volume={24},
  pages={485-498}
}
By the classical mereology I mean a theory of mereological structures in the sense of [10]. In [7] I proved that the class of these structures is not elementarily axiomatizable. In this paper a new version of this result is presented, which according to my knowledge is the first such presentation in English. A relation of this result to a certain Hsing-chien Tsai’s theorem from [13] is emphasized. 

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Decidability of General Extensional Mereology
The Calculus of Individuals and Its Uses