Projectivity types of torsion free Abelian groups of rank 1
Stimulated by a paper of \textit{R. Baer} [Am. J. Math. 61, 1-44 (1939; Zbl 0020.34704)] and a paper of \textit{E. Gasparini} and \textit{C. Metelli} [Boll. Unione Mat. Ital., VI. Ser., A 3, 363-371 (1984; Zbl 0578.20049)], the author considers projectivities between torsion-free groups of rank 1 (and of splitting mixed groups of torsion-free rank 1). He defines a new equivalence relation on types, which holds if and only if the corresponding torsion-free groups of rank 1 are projective. The earlier equivalence relation by Gasparini and Metelli is only necessary for projectivity. In the second part of this paper, the author extends his result to the mixed case, mentioned above.
scientific article; zbMATH DE number 60488