Abstract
We establish some of the basic model theoretic facts about the Gurarij operator system GS recently constructed by the second-named author. In particular, we show: (1) GS is the unique separable 1-exact existentially closed operator system; (2) GS is the unique separable nuclear model of its theory; (3) every embedding of GS into its ultrapower is elementary; (4) GS is the prime model of its theory; and (5) GS does not have quantifier-elimination, whence the theory of operator systems does not have a model companion. We also show that, for any q ∈ ℕ, the theories of Mq-spaces and Mq-systems do have a model companion, namely the Fra¨ıssé limit of the class of finite-dimensional Mq-spaces and Mq-systems respectively; moreover, we show that the model companion is separably categorical. We conclude the paper by showing that no C* algebra can be existentially closed as an operator system.
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Goldbring’s work was partially supported by NSF CAREER grant DMS-1349399. Lupini’s work was supported by the York University Susan Mann Dissertation Scholarship and by the ERC Starting grant no. 259527 of Goulnara Arzhantseva. This work was initiated during a visit of the second author to the University of Illinois at Chicago. The hospitality of the UIC Mathematics Department is gratefully acknowledged.
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Goldbring, I., Lupini, M. Model-theoretic aspects of the Gurarij operator system. Isr. J. Math. 226, 87–118 (2018). https://doi.org/10.1007/s11856-018-1691-3
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DOI: https://doi.org/10.1007/s11856-018-1691-3