Abstract
Let U be an initial segment of \(^*{\mathbb N}\) closed under addition (such U is called a cut) with uncountable cofinality and A be a subset of U, which is the intersection of U and an internal subset of \(^*{\mathbb N}\). Suppose A has lower U-density α strictly between 0 and 3/5. We show that either there exists a standard real \(\epsilon\) > 0 and there are sufficiently large x in A such that | (A+A) ∩ [0, 2x]| > (10/3+\(\epsilon\)) | A ∩ [0, x]| or A is a large subset of an arithmetic progression of difference greater than 1 or A is a large subset of the union of two arithmetic progressions with the same difference greater than 2 or A is a large subset of the union of three arithmetic progressions with the same difference greater than 4.
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Jin, R. Inverse problem for cuts. Logic and Analysis 1, 61–89 (2007). https://doi.org/10.1007/s11813-007-0002-9
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DOI: https://doi.org/10.1007/s11813-007-0002-9