Abstract:
Existence criteria for invariant and projectively invariant measures are obtained for a group $G$ of homeomorphisms of the line. These criteria are formulated in terms of the commutator subgroup $[G,G]$. For the special (but very important) case of groups of homeomorphisms of the line containing a freely acting element we obtain a criterion for the existence of a projectively invariant measure in the form of the absence of a special subgroup with two generators in which one of the generating elements is a freely acting element.
Bibliography: 20 titles.
Keywords:groups of homeomorphisms of the line (the circle), invariant measure, projectively invariant measures.