1. R. Baer, Abelian groups without elements of finite order. Duke Math. J.3, 68?122 (1937).
2. L.Fuchs, Abelian Groups. Budapest 1958.
3. I. Kaplansky, Projective modules. Ann. of Math.68, 371?377 (1958).
4. L. Ya. Kulikov, On direct decompositions of groups [Russian]. Ukrain. Math. ?.4, 230?275 and 347?372 (1952).
5. E. C. Lyapin, On the decomposition of abelian groups into direct sums of rank one groups [Russian]. Mat. Sb.8, 205?237 (1940).