MathDB
Hamiltonian cycle in distance of sets graph

Source: 2023 4th OMpD LU P3 - Brazil - Olimpíada Matemáticos por Diversão

September 21, 2023
graph theorySetscombinatoricshamiltonian cyclePower setinduction

Problem Statement

Let mm and nn be positive integers integers such that 2m+1<n2m + 1 < n, and let SS be the set of the 2n2^n subsets of {1,2,,n}\{1,2,\ldots,n\}. Prove that we can place the elements of SS on a circle, so that for any two adjacent elements AA and BB, the set AΔBA \Delta B has exactly 2m+12m + 1 elements.
Note: AΔB=(AB)(AB)A \Delta B = (A \cup B) - (A \cap B) is the set of elements that are exclusively in AA or exclusively in BB.