AI 中文总结
针对有限字母表上单词的子序列计数序列的对数凹性，Chase曾用三角阵列方法证明，本文提出基于首字母分解为加权平均的简化证明方法。
AI 中文摘要
给定有限字母表上的一个单词，考虑对每个长度计数其不同子序列数量的序列。1976年，Chase证明该序列是对数凹的，其证明使用了由单词前缀索引的三角阵列，并细致分析了多个和的比值。我们则依据首字母进行分解，将证明简化为加权平均。
英文摘要
Given a word over a finite alphabet, consider the sequence that counts, for each length, the number of distinct subsequences of that length. In 1976, Chase proved that this sequence is log-concave. His proof uses a triangular array indexed by the prefixes of the word together with a meticulous analysis of ratios of several sums. We instead decompose according to the first letter, which reduces the proof to a weighted average.
