Find a finite set 𝐴 and 𝐵⊂2𝐴 such that any element of 𝐴 is covered by at least 100 sets in 𝐵, but 𝐵 cannot be partitioned into 2 disjoint sets, each covering 𝐴.

Gaige Haynes

Gaige Haynes

Answered question

2022-09-05

Find a finite set A and B 2 A such that any element of A is covered by at least 100 sets in B, but B cannot be partitioned into 2 disjoint sets, each covering A.

Answer & Explanation

gasskadeu7

gasskadeu7

Beginner2022-09-06Added 21 answers

This is a classic/folklore puzzle.
You have 12 apostles and a messiah sitting around a circular table every night for supper.
Can it be so arranged that every night each person gets to sit with different people immediately to the left and right? Try to give a construction which achieves the maximum possible number of nights. What is the maximum possible number?
This basically boils down to decomposing K 13 (the complete graph on 13 vertices) into hamiltonian cycles.

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