385 research outputs found

    Surgery description of colored knots

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    The pair (K,r) consisting of a knot K and a surjective map r from the knot group onto a dihedral group is said to be a p-colored knot. D. Moskovich conjectured that for any odd prime p there are exactly p equivalence classes of p-colored knots up to surgery along unknots in the kernel of the coloring. We show that there are at most 2p equivalence classes. This is a vast improvement upon the previous results by Moskovich for p=3, and 5, with no upper bound given in general. T. Cochran, A. Gerges, and K. Orr, in "Dehn surgery equivalence relations of 3-manifolds", define invariants of the surgery equivalence class of a closed 3-manifold M in the context of bordisms. By taking M to be 0-framed surgery of the 3-sphere along K we may define Moskovich's colored untying invariant in the same way as the Cochran-Gerges-Orr invariants. This bordism definition of the colored untying invariant will be then used to establish the upper bound.Comment: 41 pages, 23 figures (Version 3) Minor revisions and typos fixed. Proofs of Propositions 4.1 and 4.8 revise

    The Betti numbers of some finite racks

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    We show that the lower bounds for Betti numbers given in (J. Pure Appl. Algebra 157 (2001) 135) are equalities for a class of racks that includes dihedral and Alexander racks. We confirm a conjecture from the same paper by defining a splitting for the short exact sequence of quandle chain complexes. We define isomorphisms between Alexander racks of certain forms, and we also list the second and third homology groups of some dihedral and Alexander quandles. © 2002 Elsevier Science B.V. All rights reserved

    On a theorem of murasug

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    Let l=k1⋃k2be a 2-component link in S3with k2unknotted. The 2-fold cover of S3branched over k2is again S8; let k1(2) be the inverse image of k1and suppose that k1(2) is connected. How are the signatures σ(k1), σ(K1)(2) of the knots k1and K1(2)related? This question was considered (from a slightly different point of view) by Murasugi, who gave the following answer [Topology, 9 (1970), 283-298]. © 1979, University of California, Berkeley. All Rights Reserved

    Incompressible planar surfaces in 3-manifolds

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    Let M be an orientable 3-manifold and T a torus component of ∂M. We show that the boundary-slopes of incompressible, boundary-incompressible planar surfaces (P,∂P)⊂(M,T) are pairwise within distance 4; in particular, there are at most six such boundary-slopes. A corollary is that, for any knot K in S3, at most six Dehn surgeries on K can yield a reducible 3-manifold. © 1984
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