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Published online by Cambridge University Press: 20 November 2018
Let $\tilde{M}$ be a regular branched cover of a homology 3-sphere
$M$ with deck group
$G\cong \mathbb{Z}_{2}^{d}$ and branch set a trivalent graph
$\Gamma $ ; such a cover is determined by a coloring of the edges of
$\Gamma $ with elements of
$G$ . For each index-2 subgroup
$H$ of
$G,\,{{M}_{H}}=\tilde{M}/H$ is a double branched cover of
$M$ . Sakuma has proved that
${{H}_{1}}\left( {\tilde{M}} \right)$ is isomorphic, modulo 2-torsion, to
${{\oplus }_{H}}{{H}_{1}}\left( {{M}_{H}} \right)$ , and has shown that
${{H}_{1}}\left( {\tilde{M}} \right)$ is determined up to isomorphism by
${{\oplus }_{H}}{{H}_{1}}\left( {{M}_{H}} \right)$ in certain cases; specifically, when
$d=2$ and the coloring is such that the branch set of each cover
${{M}_{H}}\to M$ is connected, and when
$d=3$ and
$\Gamma $ is the complete graph
${{K}_{4}}$ . We prove this for a larger class of coverings: when
$d=2$ , for any coloring of a connected graph; when
$d=3\,\text{or}\,\text{4}$ , for an infinite class of colored graphs; and when
$d=5$ , for a single coloring of the Petersen graph.