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Let M be a complete, finite-volume, orientable hyperbolic manifold
having exactly one cusp. If we assume that π1(M) has no
subgroup isomorphic to a genus–2 surface group and that either
(a)
dimZpH1(M;Zp)≥
5 for some prime p, or (b)
dimZ2H1(M;Z2)≥
4, and the subspace of H2(M;Z2) spanned
by the image of the cup product
H1(M;Z2)×
H1(M;Z2)→
H2(M;Z2) has dimension at most 1, then
vol M > 5.06. If we assume that
dimZ2H1(M;Z2)≥
7 and that the compact core N of M contains a genus–2 closed
incompressible surface, then vol M > 5.06. Furthermore, if we assume
only that
dimZ2H1(M;Z2)≥
7, then vol M > 3.66.
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