Certified $Σ_1$-sentences

Abstract

In this paper, we study the employment of $\Sigma_1$-sentences with certificate, i.e., $\Sigma_1$-sentences where a number of principles is added to ensure that the witness is sufficiently number-like. We develop certificates in some detail and illustrate their use by reproving some classical results and proving some new ones. An example of such a classical result is Vaught's theorem of the strong effective inseparability of ${\sf R}_0$. We also develop the new idea of a theory being ${\sf R}_{0{\sf p}}$-sourced. Using this notion we can transfer a number of salient results from ${\sf R}_0$ to a variety of other theories.