Geodesic
On direct sums of $\text{B}^{(1)}$-groups -- II
Commentationes Mathematicae Universitatis Carolinae, Tome 47 (2006) no. 2, pp. 189-202.

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$\operatorname{B}^{(1)}$-groups are a class of torsionfree Abelian groups of finite rank, part of the main class of Butler groups. In the paper C. Metelli, {\it On direct sums of $\operatorname{B}^{(1)}$-groups\/}, Comment. Math. Univ. Carolinae {\bf 34} (1993), 587--591, the problem of direct sums of $\operatorname{B}^{(1)}$-groups was discussed, and a necessary and sufficient condition was given for the direct sum of two $\operatorname{B}^{(1)}$-groups to be a $\operatorname{B}^{(1)}$-group. While sufficiency holds, necessity was wrongly claimed; we solve here the problem, and in the process study a curious hierarchy among indecomposable direct summands of $\operatorname{B}^{(1)}$-groups.
Classification : 20K15
Keywords: Butler group; $\operatorname{B}^{(1)}$-group; tent; direct decomposition; finite algorithm 
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     title = {On direct sums of $\text{B}^{(1)}$-groups -- {II}},
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De Vivo, Clorinda; Metelli, Claudia. On direct sums of $\text{B}^{(1)}$-groups -- II. Commentationes Mathematicae Universitatis Carolinae, Tome 47 (2006) no. 2, pp. 189-202. http://geodesic.mathdoc.fr/item/CMUC_2006__47_2_a0/