The paper presents four open problems. One concerns a possible converse to Tarski's undefinability of truth theorem, and is of a general character. The other three are more specific. The questions are about some special $\omega_1$-like models, initial segments of countable recursively saturated models of PA, and about extendability of automorphisms. In each case a partial answer is given. All partial solutions are based on applications of inductive satisfaction classes.
"Four Problems Concerning Recursively Saturated Models of Arithmetic." Notre Dame J. Formal Logic 36 (4) 519 - 530, Fall 1995. https://doi.org/10.1305/ndjfl/1040136913