CERTIFIED $ \Sigma _1$-SENTENCES

Abstract In this paper, we study the employment of $\Sigma _1$ -sentences with certificates, 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 $\mathsf {R}_0$ . We also develop the new idea of a theory being $\mathsf {R}_{0\mathsf {p}}$ -sourced . Using this notion, we can transfer a number of salient results from $\mathsf {R}_0$ to a variety of other theories.