Abstract
We present a short and direct proof (based on the Pontryagin-Thom construction) of the following Pontryagin-Steenrod-Wu theorem: (a) LetM be a connected orientable closed smooth (n + 1)-manifold,n≥3. Define the degree map deg: πn(M) →H n(M; ℤ) by the formula degf =f*[S n], where [S n] εH n(M; ℤ) is the fundamental class. The degree map is bijective, if there existsβ εH 2(M, ℤ/2ℤ) such thatβ ·w 2(M) ε 0. If suchβ does not exist, then deg is a 2-1 map; and (b) LetM be an orientable closed smooth (n+2)-manifold,n≥3. An elementα lies in the image of the degree map if and only ifρ 2 α ·w 2(M)=0, whereρ 2: ℤ → ℤ/2ℤ is reduction modulo 2.
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References
B. A. Dubrovin, S. P. Novikov and A. T. Fomenko,Modern Geometry: Methods and Applications, Nauka, Moscow, 1979 (in Russian).
A. T. Fomenko and D. B. Fuchs,A Course in Homotory Theory, Nauka, Moscow, 1989 (in Russian).
L. S. Pontryagin,Homologies in compact Lie groups, Matematicheskii Sbornik6 (1939), no. 3, 389–422.
N. E. Steenrod,Products of cocycles and extensions of mappings, Annals of Mathematics (2)48 (1947), 290–320.
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Repovš, D., Skopenkov, M. & Spaggiari, F. On the pontryagin-steenrod-wu theorem. Isr. J. Math. 145, 341–347 (2005). https://doi.org/10.1007/BF02786699
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DOI: https://doi.org/10.1007/BF02786699