EXISTENTIALLY CLOSED MODELS IN THE FRAMEWORK OF ARITHMETIC
Zofia Adamowicz, Andrés Cordón–Franco, Francisco Martín · Journal of Symbolic Logic · 2016
Abstract We prove that the standard cut is definable in each existentially closed model ofIΔ0+ exp by a (parameter free) П1–formula. This definition is optimal with respect to quantifier complexity and allows us to improve some previously known results on existentially closed models of fragments of arithmetic.