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Let $(X,d)$ be a compact, connected, locally connected, locally compact metric space.

A result of Bing and Moise (independently) states that $(X,d)$ admits a topology preserving convex metric i.e., a metric $d'$ such that if $p,q \in X$, there exists a point $r\in X$ such that $d'(p,r) = d'(q,r) = d'(p,q)/2$.

I would like to understand the construction of the convex metric $d'$.

The main point that I can gather is that, the authors define a sequence $E_1(p,q),\, E_2(p,q),\dots$ of functions on pairs of points of $X$ such that $E(p,q) = \lim E_i(p,q)$ is a convex metric on $X$.

However, I do not understand how to explicitly compute these $E_i(p,q)$, as the proofs of Bing and Moise are rather complicated and involved.

Question. Can someone explain how to explicitly compute these $E_i(p,q)$? Or provide a less technical description of these $E_i(p,q)$? Or provide a reference to where this convex metric is unraveled a bit?

Thanks!

References

Bing, Partitioning a Set, Bull. Amer. Math Soc., Vol 55 (1949) pp. 1101-1110

Moise, Grille decomposition and convexification theorems for compact locally connected continua, Bull. Amer. Math Soc., Vol 55 (1949) pp. 1111-1121

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As far as I know the most accessible proof of Bing's construction is in Section 2 of the paper:

J. C. Mayer, L. G. Oversteegen, E, D. Tymchatyn, The Menger curve. Characterization and extension of homeomorphisms of non-locally-separating closed subsets. Dissertationes Math. (Rozprawy Mat.) 252 (1986), 45 pp.

The paper can be downloaded from:

http://pldml.icm.edu.pl/pldml/element/bwmeta1.element.zamlynska-1d60f6d5-8102-4734-9186-d4b4bfd8f2dc

The paper does not address construction of a convex metric, but many years ago I wanted to learn the proof of the existence of a convex metric (I never did) and this is what Tymchatyn wrote to me (in 2007):

Once you have appropriate partitions the construction of a convex metric is relatively easy. Bing's 1952 BAMS paper Partitioning Continuous Curves is the place to read it.

There is a proof of the partitioning theorem for Peano continua in the book of Hall and Spencer,Elementary Topology,Wiley,1955. As I recall the proof there is the one given by Bing. The first part of Bing's proof can be simplified a bit using a Peano map of the interval onto a Peano continuum $X$ to get a decomposition of $X$ into finitely many nice bricks between a closed subset $A$ of $X$ and a point $p$ outside $A$.

Bing assigns weights to elements in a defining sequence of partitions $U_i$ of $X$ in such a way that shortest chains in the partitions between two points converge to a distance which gives the convex metric.

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  • $\begingroup$ Dear Piotr, thank you for the reference! It does help with understanding more about the definitions in the Bing and Moise paper, however it does not seem to address the convex metric construciton $\endgroup$ Commented Oct 30, 2019 at 18:50
  • $\begingroup$ @JacksonMorrow I updated my answer. I do not know if it helps. $\endgroup$ Commented Oct 31, 2019 at 21:11
  • $\begingroup$ @ Piotr Hajlasz Thank you for the update! This is very very useful. I did not understand the reasoning for the partitions, but this makes it much clearer. Thank you! $\endgroup$ Commented Nov 4, 2019 at 19:11

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