Resumen de Finitely generated groups and first-order logic

A. Morozov, André Nies

• It is proved that the following classes of finitely generated groups have -complete first-order theories: all finitely generated groups, the -generated groups, and the strictly -generated groups (). Moreover, all those theories are distinct. Similar techniques show that quasi-finitely axiomatizable groups have a hyperarithmetical word problem, where a finitely generated group is quasi-finitely axiomatizable if it is the only finitely generated group satisfying an appropriate first-order sentence. The Turing degrees of word problems of quasi-finitely axiomatizable groups form a cofinal set in the Turing degrees of hyperarithmetical sets.