Tarski's problem about the elementary theory of free groups has a positive solution.
The classical decision problem and partial functions.
The decidability of some -categorical theories
The diophantine theory of a ring of analytic functions.
The elementary theory of Abelian groups with m-chains of pure subgroups
The join of equational theories
The -theory of profinite abelian groups
The monadic second-order logic of graphs III : tree-decompositions, minors and complexity issues
The positivity problem for fourth order linear recurrence sequences is decidable
The problem whether each element of a sequence satisfying a fourth order linear recurrence with integer coefficients is nonnegative, referred to as the Positivity Problem for fourth order linear recurrence sequence, is shown to be decidable.
The pseudovariety is hyperdecidable
The recursive sets in certain monadic second order fragments of arithmetic.
The second-order monadic theory of the free inverse monoid is undecidable. (La théorie monadique du second ordre du monoïde inversif libre est indécidable.)
The theory of abelian p-groups with the quantifier I is decidable
The theory of Archimedean real closed fields in logics with Ramsey quantifiers
The theory of boolean algebras with a distinguished subalgebra is undecidable
The theory of differentially closed fields in logics with cardinal quantifiers.
The Theory of Successor with an Extra Predicate.
The Undecidability of Pseudo Real Closed Fields.
Théorie des modèles pour des anneaux de fonctions entières et des corps de fonctions méromorphes
Theorien abelscher Gruppen mit einem einstelligen Prädikat