For integers 4 ≤ k < l, some difference occurs three times in {0, ±1, ±k, ±l} iff l ∈ {k+1, k+2, 2k−1, 2k, 2k+1, 3k}

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For integers 4 ≤ k < l, some difference occurs three times in {0, ±1, ±k, ±l} iff l ∈ {k+1, k+2, 2k−1, 2k, 2k+1, 3k} · Prove2Me