On “simple” undecidable fragments of positive and elementary theories of free semigroups of finite or countable rank
Valery Georgievich Durnev, О. В. Зеткина, Алена Игоревна Зеткина · Journal of Physics Conference Series · 2020
Abstract We establish algorithmic undecidability of “simple” (with respect to the quantifier-prefix and the quantifier-free part of the formulas) fragments of positive theories of finitely generated semigroups and elementary theory of a free countably generated semigroup.