Decidability of the mixed quantifier fragment for powers of two and three

Determine whether the \(\exists^*\forall^*\) fragment of the first-order theory of \(\langle\mathbb{N};0,1,<,+,\{2^n:n\in\mathbb{N}\},\{3^n:n\in\mathbb{N}\}\rangle\) is decidable.

Background

The paper discusses the structure obtained by expanding Presburger arithmetic with the predicates of powers of two and powers of three. The full first-order theory is known to be undecidable, while the existential fragment is known to be decidable. The cited results leave the intermediate \exists^*\forall^* fragment unresolved.

References

Decidability thus remains open for the $\exists* \forall*$ fragment.

Rich Sequences and Decidability of Arithmetic Theories  (2609.20415 - Karimov et al., 17 Sep 2026) in Footnote in Section 1, State of the art for Problem 1