Bing–Borsuk conjecture

In mathematics, the Bing–Borsuk conjecture states that every ${\displaystyle n}$-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.

Definitions

A topological space is homogeneous if, for any two points ${\displaystyle m_{1},m_{2}\in M}$, there is a homeomorphism of ${\displaystyle M}$ which takes ${\displaystyle m_{1}}$ to ${\displaystyle m_{2}}$.

A metric space ${\displaystyle M}$ is an absolute neighborhood retract (ANR) if, for every closed embedding ${\displaystyle f:M\rightarrow N}$ (where ${\displaystyle N}$ is a metric space), there exists an open neighbourhood ${\displaystyle U}$ of the image ${\displaystyle f(M)}$ which retracts to ${\displaystyle f(M)}$.[1]

There is an alternate statement of the Bing–Borsuk conjecture: suppose ${\displaystyle M}$ is embedded in ${\displaystyle \mathbb {R} ^{m+n}}$ for some ${\displaystyle m\geq 3}$ and this embedding can be extended to an embedding of ${\displaystyle M\times (-\varepsilon ,\varepsilon )}$. If ${\displaystyle M}$ has a mapping cylinder neighbourhood ${\displaystyle N=C_{\varphi }}$ of some map ${\displaystyle \varphi$ :\partial N\rightarrow M} with mapping cylinder projection ${\displaystyle \pi :N\rightarrow M}$, then ${\displaystyle \pi }$ is an approximate fibration.[2]

History

The conjecture was first made in a paper by R. H. Bing and Karol Borsuk in 1965, who proved it for ${\displaystyle n=1}$ and 2.[3]

Włodzimierz Jakobsche showed in 1978 that, if the Bing–Borsuk conjecture is true in dimension 3, then the Poincaré conjecture must also be true.[4]

The Busemann conjecture states that every Busemann ${\displaystyle G}$-space is a topological manifold. It is a special case of the Bing–Borsuk conjecture. The Busemann conjecture is known to be true for dimensions 1 to 4.

References

1. M., Halverson, Denise; Dušan, Repovš, (23 December 2008). "The Bing–Borsuk and the Busemann conjectures". Mathematical Communications. 13 (2). ISSN 1331-0623.CS1 maint: extra punctuation (link)
2. Daverman, R. J.; Husch, L. S. (1984). "Decompositions and approximate fibrations". The Michigan Mathematical Journal. 31 (2): 197–214. doi:10.1307/mmj/1029003024. ISSN 0026-2285.
3. Bing, R. H.; Armentrout, Steve (1998). The Collected Papers of R. H. Bing. American Mathematical Soc. p. 167. ISBN 9780821810477.
4. Jakobsche, W. "The Bing–Borsuk conjecture is stronger than the Poincaré conjecture". Fundamenta Mathematicae. 106 (2). ISSN 0016-2736.