"two subsequences are the same in content"
What does than mean "same in content"? Do subsequences (1, 2, 3) and (2, 1, 3) same in content?

No, two subsequences are the same in content when they are the same regarded as just integer sequences, ignoring the indices of elements. (日本語版を読んでいる方へ: この質問は無視してください。)