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  2. Retraction (topology) - Wikipedia

    en.wikipedia.org/wiki/Retraction_(topology)

    A space is an absolute neighborhood retract for the class , written ⁡ (), if is in and whenever is a closed subset of a space in , is a neighborhood retract of . Various classes C {\displaystyle {\mathcal {C}}} such as normal spaces have been considered in this definition, but the class M {\displaystyle {\mathcal {M}}} of metrizable spaces ...

  3. Borsuk–Ulam theorem - Wikipedia

    en.wikipedia.org/wiki/Borsuk–Ulam_theorem

    The Borsuk–Ulam theorem is equivalent to the following statement: A continuous odd function from an n-sphere into Euclidean n-space has a zero. PROOF: PROOF: If the theorem is correct, then it is specifically correct for odd functions, and for an odd function, g ( − x ) = g ( x ) {\displaystyle g(-x)=g(x)} iff g ( x ) = 0 {\displaystyle g(x ...

  4. Using the Borsuk–Ulam Theorem - Wikipedia

    en.wikipedia.org/wiki/Using_the_Borsuk–Ulam...

    Using the Borsuk–Ulam Theorem: Lectures on Topological Methods in Combinatorics and Geometry is a graduate-level mathematics textbook in topological combinatorics. It describes the use of results in topology , and in particular the Borsuk–Ulam theorem , to prove theorems in combinatorics and discrete geometry .

  5. Karol Borsuk - Wikipedia

    en.wikipedia.org/wiki/Karol_Borsuk

    Karol Borsuk (8 May 1905 – 24 January 1982) was a Polish mathematician. His main area of interest was topology . He made significant contributions to shape theory , a term which he coined.

  6. Section (category theory) - Wikipedia

    en.wikipedia.org/wiki/Section_(category_theory)

    The concept in topology was defined by Karol Borsuk in 1931. [ 2 ] Borsuk's student, Samuel Eilenberg , was with Saunders Mac Lane the founder of category theory, and (as the earliest publications on category theory concerned various topological spaces) one might have expected this term to have initially be used.

  7. Borsuk's conjecture - Wikipedia

    en.wikipedia.org/wiki/Borsuk's_conjecture

    [7] For all n for fields of revolution — shown by Boris Dekster (1995). [8] The problem was finally solved in 1993 by Jeff Kahn and Gil Kalai, who showed that the general answer to Borsuk's question is no. [9] They claim that their construction shows that n + 1 pieces do not suffice for n = 1325 and for each n > 2014.

  8. Bing–Borsuk conjecture - Wikipedia

    en.wikipedia.org/wiki/Bing–Borsuk_conjecture

    In mathematics, the Bing–Borsuk conjecture states that every -dimensional homogeneous absolute neighborhood retract space is a topological manifold. The conjecture has been proved for dimensions 1 and 2, and it is known that the 3-dimensional version of the conjecture implies the Poincaré conjecture .

  9. Tucker's lemma - Wikipedia

    en.wikipedia.org/wiki/Tucker's_lemma

    In mathematics, Tucker's lemma is a combinatorial analog of the Borsuk–Ulam theorem, named after Albert W. Tucker. Let T be a triangulation of the closed n-dimensional ball. Assume T is antipodally symmetric on the boundary sphere.