Ultraproducts and Chevalley groups

Given a simple non-trivial finite-dimensional Lie algebra L, fields and Chevalley groups , we first prove that is isomorphic to . Then we consider the case of Chevalley groups of twisted type . We obtain a result analogous to the previous one. Given perfect fields having the property that any element is either a square or the opposite of a square and Chevalley groups , then is isomorphic to . We apply our results to prove the decidability of the set of sentences true in almost all finite groups of the form L(K) where K is a finite field and L a fixed untwisted Chevalley type. Received: 19 November 1993 / Revised version: 15 November 1995