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单词 LoopTheorem
释义

loop theorem


In the topologyMathworldPlanetmath of 3-manifolds, the loop theorem is generalizationPlanetmathPlanetmath of an ansatz discovered by Max Dehn (namely, Dehn’s lemma),who saw that if a continuous map from a 2-disk to a 3-manifold whose restrictionPlanetmathPlanetmathPlanetmath to the boundary’s disk has no singularities,then there exists another embeddingMathworldPlanetmathPlanetmathPlanetmath whose restriction to the boundary’s disk is equal to the boundary’s restriction original map.

The following statement called the loop theorem is a version from J. Stallings, but written in W. Jaco’s book.

Let M be a three-manifold and let Sbe a connected surface in M. Let Nπ1(M) be a normal subgroupMathworldPlanetmath.Let f:D2Mbe a continuous map such that f(D2)Sand [f|D2]N.
Then there exists an
embeddingg:D2M such thatg(D2)Sand[g|D2]N,

The proof is a clever construction due to C. Papakyriakopoulos about a sequence (a tower) of covering spaces.Maybe the best detailed presentationMathworldPlanetmathPlanetmathPlanetmath is due to A. Hatcher.But in general, accordingly to Jaco’s opinion, ”… for anyone unfamiliar with the techniques of 3-manifold-topology and are here to gain a working knowledge for the study of problems in this…, there is no better to start.”

References

W. Jaco, Lectures on 3-manifolds topology, A.M.S. regional conference series in Math 43.

J. Hempel, 3-manifolds, Princeton University Press 1976.

A. Hatcher, Notes on 3-manifolds, available on-line.

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