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MathNet 2016-part-03 — 184 problems (EN–VI) Question 89

Math Olympiad Vault · MathNet 2016-part-03 — 184 problems (EN–VI)

Question 89

A set $S = \{s_1, \dots, s_k\}$ of positive real numbers is *polygonal* if $k \ge 3$ and there is a non-degenerate planar $k$-gon whose side lengths are exactly $s_1, \dots, s_k$; the set $S$ is *multipolygonal* if in every partition of $S$ into two subsets, each of which has at least three elements, exactly one of these two subsets is polygonal. Fix an integer $n \ge 7$.

a) Does there exist an $n$-element multipolygonal set, removal of whose maximal element leaves a multipolygonal set?