The subtle behavior of the facial distance


We give a simple example that disproves the following 2015 conjecture of Lacoste-Julien and Jaggi concerning the pyramidal width (aka facial distance):

The pyramidal width of a set of vertices is non-increasing when another vertex is added (assuming that all previous points remain vertices).

In contrast to the recent example by Zhao (arXiv:2607.29555), our counterexample is readily verifiable via visual inspection. Furthermore, our counterexample shows that the relative increase in the pyramidal width can be arbitrarily large.

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