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IMO Shortlist 2012, Algebra 2

Source: IMO Shortlist 2012, Algebra 2

July 29, 2013
number theorymodular arithmeticIMO Shortlist

Problem Statement

Let Z\mathbb{Z} and Q\mathbb{Q} be the sets of integers and rationals respectively. a) Does there exist a partition of Z\mathbb{Z} into three non-empty subsets A,B,CA,B,C such that the sets A+B,B+C,C+AA+B, B+C, C+A are disjoint? b) Does there exist a partition of Q\mathbb{Q} into three non-empty subsets A,B,CA,B,C such that the sets A+B,B+C,C+AA+B, B+C, C+A are disjoint?
Here X+YX+Y denotes the set {x+y:xX,yY}\{ x+y : x \in X, y \in Y \}, for X,YZX,Y \subseteq \mathbb{Z} and for X,YQX,Y \subseteq \mathbb{Q}.