English: The 8-element set {1, 2, 4, 5, 10, 11, 13, 14} is a Salem–Spencer set, meaning that it has no three elements forming an arithmetic progression. For each pair of two numbers from the set, their midpoint (one of the 28 yellow points) is outside the set, preventing those two numbers from being the first and last element of an arithmetic progression.
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An 8-element Salem–Spencer set
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3 February 2019
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