April’s Issue 1 of Volume XXVIII was a Special Issue with pioneering essays by Aubrey D.N.J. de Grey, who constructs the first ever 5-chromatic unit-distance graph; Marijn J.H. Heule, who sets 6 consecutive world records in reducing the size of such graphs; and Geoffrey Exoo and Dan Ismailescu, who are arming themselves – and us – with tools for the next big step.

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By G. Exoo and D. Ismailescu
By G. Exoo and D. Ismailescu

This is Exoo’s and Ismailescu’s triangle-free, 4 chromatic unit distance graph of order 17 – a World Record.

It comes from the essay “Small Order Triangle-Free 4 Chromatic Unit Distance Graphs” that appear in the October issue (2) of Volume XXVI.