a1 Department of Mathematics, California Institute of Technology, Pasadena, CA 91125, USA
It has been shown by J. Feldman, P. Hahn and C. C. Moore that every non-singular action of a second countable locally compact group has a countable (in fact so-called lacunary) complete measurable section. This is extended here to the purely Borel theoretic category, consisting of a Borel action of such a group on an analytic Borel space (without any measure). Characterizations of when an arbitrary Borel equivalence relation admits a countable complete Borel section are also established.
(Received March 01 1991)
† Research partially supported by a NSF Grant DMS-9020153.