Richard D. Byrd,1Justin T. Lloyd,1Roberto A. Mena,1and J. Roger Teller1
Received18 Jun 1979
Revised29 Feb 1980
Abstract
In this paper a condition, which is necessary and sufficient, is determined when a retraction of a subgroup H of a torsion-free group G can be extended to a retraction of G. It is also shown that each retraction of a torsion-free abelian group can be uniquely extended to a retraction of its divisible closure.