1. 1. P. Hill, Ulm’s theorem for totally projective groups, Notices Amer. Math. Soc. 14 (1967), 940.
2. Direct sums of countable groups;Kolettis, George, Jr.;Duke Math. J.,1960
3. Homology and direct sums of countable abelian groups;Nunke, R. J.;Math. Z.,1967