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On the pontryagin-steenrod-wu theorem

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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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Correspondence to Dušan Repovš.

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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

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