Cauchy subsequences and hulls of sequences in labeled trees
Let be a tree, and let be a sequence of distinct vertices of . For a set of vertices, its hull is the corresponding minimal connected subgraph. A labeling is non-degenerate in the sense used for the ultrametric induced by .
Cauchy-hull conjecture. The following conditions are equivalent:
- The hull of the range set of is a union of a ray with some finite tree.
- For every non-degenerate , the existence of a Cauchy subsequence of implies that is itself a Cauchy sequence.
This conjecture links the geometry of the hull of a sequence's range to the behavior of Cauchy subsequences in the ultrametrics induced by labelings. Its resolution status is not specified in the source.
References
Primary source
Oleksiy Dovgoshey and Mehmet Küçükaslan, “Labeled trees generating complete, compact, and discrete ultrametric spaces”, arXiv:2101.00626 (2022).
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