Geodesic
Cohomology of $BO(n_1)\times \dots \times BO(n_m)$ with local integer coefficients
Commentationes Mathematicae Universitatis Carolinae, Tome 46 (2005) no. 1, pp. 21-32 Cet article a éte moissonné depuis la source Czech Digital Mathematics Library

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Let $\Cal Z$ be a set of all possible nonequivalent systems of local integer coefficients over the classifying space $BO(n_1)\times \dots \times BO(n_m)$. We introduce a cohomology ring $\bigoplus_{\Cal G\in \Cal Z} H^*(BO(n_1)\times \dots \times BO(n_m);\Cal G)$, which has a structure of a $\Bbb Z\oplus (\Bbb Z_2)^m$-graded ring, and describe it in terms of generators and relations. The cohomology ring with integer coefficients is contained as its subring. This result generalizes both the description of the cohomology with the nontrivial system of local integer coefficients of $BO(n)$ in [Č] and the description of the cohomology with integer coefficients of $BO(n_1)\times \dots \times BO(n_m)$ in [M].
Let $\Cal Z$ be a set of all possible nonequivalent systems of local integer coefficients over the classifying space $BO(n_1)\times \dots \times BO(n_m)$. We introduce a cohomology ring $\bigoplus_{\Cal G\in \Cal Z} H^*(BO(n_1)\times \dots \times BO(n_m);\Cal G)$, which has a structure of a $\Bbb Z\oplus (\Bbb Z_2)^m$-graded ring, and describe it in terms of generators and relations. The cohomology ring with integer coefficients is contained as its subring. This result generalizes both the description of the cohomology with the nontrivial system of local integer coefficients of $BO(n)$ in [Č] and the description of the cohomology with integer coefficients of $BO(n_1)\times \dots \times BO(n_m)$ in [M].
Classification : 55N25, 55R40, 55R45
Keywords: singular cohomology with local coefficients 
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     author = {Lastovecki, Richard},
     title = {Cohomology of $BO(n_1)\times \dots \times BO(n_m)$ with local integer coefficients},
     journal = {Commentationes Mathematicae Universitatis Carolinae},
     pages = {21--32},
     year = {2005},
     volume = {46},
     number = {1},
     mrnumber = {2175856},
     zbl = {1121.55012},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/CMUC_2005_46_1_a2/}
}
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Lastovecki, Richard. Cohomology of $BO(n_1)\times \dots \times BO(n_m)$ with local integer coefficients. Commentationes Mathematicae Universitatis Carolinae, Tome 46 (2005) no. 1, pp. 21-32. http://geodesic.mathdoc.fr/item/CMUC_2005_46_1_a2/