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Published online by Cambridge University Press: 01 September 2008
Let n ≥ 1 be an integer. Given a vector a=(a1,. . ,an)∈, write (the ‘projection of a onto the positive orthant’). For a set A⊆ put A+:={a+: a ∈ A} and A−A:={a−b: a, b ∈ A}. Improving previously known bounds, we show that |(A−A)+| ≥ |A|3/5/6 for any finite set A⊆, and that |(A−A)+| ≥ c|A|6/11/(log |A|)2/11 with an absolute constant c>0 for any finite set A⊆ such that |A| ≥ 2.