The weak-similarity characterization of maximal centers of distances

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Let n∈Nn\in\mathbb{N} and let (X,d)(X,d) and (Y,ρ)(Y,\rho) be ultrametric spaces such that

∣X∣=∣Y∣=2n|X|=|Y|=2^n

and

∣C(X)∣=n+1,|C(X)|=n+1,

where C(X)C(X) denotes the center of distances of (X,d)(X,d). A bijection Φ:X→Y\Phi:X\to Y is a weak similarity if there is a strictly increasing function f:D(Y)→D(X)f:D(Y)\to D(X) such that

d(x,y)=f(ρ(Φ(x),Φ(y)))d(x,y)=f\bigl(\rho(\Phi(x),\Phi(y))\bigr)

for all x,y∈Xx,y\in X.

The weak-similarity characterization. The equality

∣C(Y)∣=∣C(X)∣|C(Y)|=|C(X)|

holds if and only if (X,d)(X,d) and (Y,ρ)(Y,\rho) are weakly similar.

This conjecture asks whether, under the maximal-cardinality condition on the center of distances, equality of the cardinalities of the centers characterizes weak similarity. The supplied text gives no resolution status.

References

Primary source

Oleksiy Dovgoshey and Olga Rovenska, “On the center of distances of finite ultrametric spaces”, arXiv:2603.25850 (2026).

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