Characterization of 2-distinguishable trees by branch orbit counts

Let TT be a tree. For a vertex ww and a neighbor xx of ww, let TxT^x denote the component containing xx after deleting ww, let μ(x)\mu(x) denote the number of isomorphism types among the branches rooted at xx, and let a(Tx)a(T^x) denote the number of distinguishing subsets of TxT^x. Characterization conjecture. The tree TT is 22-distinguishable if and only if, for any vertex ww and any neighbor xx of ww, μ(x)≤a(Tx)\mu(x)\leq a(T^x) if TxT^x is finite, and

μ(x)=2∣Tx∣\mu(x)=2^{|T^x|}

if TxT^x is infinite. This would characterize 2-distinguishable trees in terms of the number of branch types and distinguishing subsets of their rooted components, extending the preceding characterization of aa-maximum trees; the paper provides no resolution of the conjecture.

References

Primary source

Wilfried Imrich, Rafał Kalinowski, Florian Lehner, Monika Pilśniak and Marcin Stawiski, “Distinguishing finite and infinite trees of arbitrary cardinality”, arXiv:2506.14402 (2025).

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