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MathNet 2022-part-05 — 197 problems (EN–VI) Question 29

Math Olympiad Vault · MathNet 2022-part-05 — 197 problems (EN–VI)

Question 29

Let $n \ge 3$ be an integer, and consider a set of $n$ points in three-dimensional space such that:
(i) every two distinct points are connected by a string which is either red, green, blue, or yellow;
(ii) for every three distinct points, if the three strings between them are not all of the same colour, then they are of three different colours;
(iii) not all the strings have the same colour.
Find the maximum possible value of $n$.