Pseudofiniteness in Hrushovski Constructions

Abstract

In a relational language consisting of a single relation $ R, $ we investigate pseudofiniteness of certain Hrushovski constructions obtained via predimension functions. It is notable that the arity of the relation $ R $ plays a crucial role in this context. When $ R $ is ternary, by extending the methods developed in [BL12], we interpret $ \langle\mathbb{Q}^{+},<\rangle $ in the $ \langle\mathcal{K}^{+}_{0},\leq^{*}\rangle $-generic and prove that this structure is not pseudofinite. This provides a negative answer to the question posed in [EW09] (Question 2.6). This result, in fact, unfolds another aspect of complexity of this structure, along with undecidability and strict order property proved in [EW09] and [Bl12]. On the other hand, when $ R $ is binary, it can be shown that the $ \langle\mathcal{K}^{+}_{0},\leq^{*}\rangle $-generic is decidable and pseudofinite.