Dr. Aubrey wrote an article entitled “The Airplane’s Chromatic Number is at least 5” and received the David P. Robbins Award in Joint Math Meetings for his work.
This article discusses the Hadwiger-Nelson problem which asks for the minimum number of colours needed to colour the points on the plane in such a way that there are not two points at a distance from each other with the same colour. Dr. de Grey discovered a family of finite distance unit graphics on the plane that are not four-color, thus improving the lower limit of the Hadwiger-Nelson problem.
To read the article click here: https://www.researchgate.net/publication/324329156_The_chromatic_number_of_the_plane_is_at_least_5