Pop-stacks are variants of stacks that were introduced by Avis and Newborn in 1981. Coincidentally, a 1982 result of Unger implies that every permutation of length $n$ can be sorted by $n-1$ passes through a deterministic pop-stack. We give a new proof of this result inspired by Knuth’s zero-one principle.

中文翻译：

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对排列进行排序需要多少个 Pop-Stacks？

弹出堆栈是 Avis 和 Newborn 在 1981 年引入的堆栈的变体。巧合的是，Unger 的 1982 年结果意味着长度为 $n$ 的每个排列都可以按 $n-1$ 排序通过确定性弹出堆栈。我们在 Knuth 的零一原则的启发下给出了这个结果的新证明。