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x+y in B iff x,y in A

Source: China Mathematical Olympiad 2015 Q3

December 20, 2014
absolute valuecombinatorics proposedcombinatorics

Problem Statement

Let n5n \geq 5 be a positive integer and let AA and BB be sets of integers satisfying the following conditions:
i) A=n|A| = n, B=m|B| = m and AA is a subset of BB ii) For any distinct x,yBx,y \in B, x+yBx+y \in B iff x,yAx,y \in A
Determine the minimum value of mm.