On sofic groups

Abstract

Answering some questions of Weiss in [B. Weiss. Sofic groups and dynamical systems. (Ergodic theory and harmonic analysis, Mumbai, 1999.) Sankhya Ser. A. 62 (2000), 350-359.], we prove that a free product of sofic groups is sofic and that amenable extensions of sofic groups are sofic. We also give an example of a finitely generated sofic group that is not residually amenable.