Consider the set of all pairs of positive integers (A,B) in which A<B . Some of these pairs are to be designated as "black" , while the remainder are to be designated as "white" . Is it possible to designate these pairs in such a way that for any triple of positive integers of form A,A+D,A+2D, in which D>0, the associated pairs (A,A+D) , (A,A+2D) and (A+D,A+2D) would include at least one pair of each colour? ColoringcombinatoricsInteger