A characteristically simple group

Abstract

The object of this note is to give an example of an infinite locally finite p -group which has no proper characteristic subgroup except the unit group. (A group G is a locally finite p -group if every finite set of elements of G generates a subgroup of finite order equal to a power of the prime p .) It is known that an infinite locally finite p -group cannot be simple, for if it were it would satisfy the minimal condition for normal subgroups, and so have a non-trivial centre (see(1)). However our example shows that it can be characteristically-simple. Examples are known of locally finite p -groups with trivial centre ((2), (4)), and of locally finite p -groups coinciding with their commutator groups ((1), (5)). Since the centre and commutator subgroup of a group are characteristic subgroups our example will have both of these properties. We may remark that the direct product of a simple, or even of a characteristically-simple group with itself any number of times is also characteristically-simple, but by Corollary 2.1 our group cannot be so decomposed.