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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.