The weak-similarity characterization of maximal centers of distances

Let nNn\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:XY\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,yXx,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.

Sources & referencesView supporting material

Primary source

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

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