Problem 3. Suppose that s_1, s_2, s_3, ... is a strictly increasing sequence of positive integers such that the subsequence s_{s_1}, s_{s_2}, s_{s_3}, ... and s_{s_1+1}, s_{s_2+1}, s_{s_3+1}, ... are both arithmetic progressions. Prove that the sequence s_1, s_2, s_3, ... is itself an arithmetic progression.
sorry不是沒中文,只是翻得很爛 希望有興趣的人自己翻,單字很少 _________________ poseidon also likes math
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