应bat365在线平台官网登录邀请，云南大学曹春华教授将为bat365官网师生作线上学术报告。
报告题目：Rational Code Having Deciphering Delay d
报告摘要：Let X be a nonempty code with deciphering delay d. If d = 0, then X is a prefix code. Let L be the set of proper prefixes of words in X, and let L ̅= A*\ L be its complement. Let X'= L ̅\ L ̅A+. Then Y = X∪X' is a maximal prefix code containing X. If X is rational, then Y is rational. If d ≥ 1, let Q be the set of words having no prefix in X and which are not a factor of any word in X. Now, let P be the set of words in Q which are minimal for the prefix order: P = Q\QA+. Note that P is a prefix code. Moreover, words in P and X are incomparable for the prefix order.
We say that a pair (w,p) ∈X*×P is good if w is the longest prefix in X* of wp. Note that if (w,p) is good, then this pair is completely determined by the word wp. Note also that any pair (1,p) for p∈P is good. We say that the pair (w,p) ∈X*× P is very good if (uw,p) is good for any u∈X*. Note that if (w,p) is very good, then so is (uw,p) for any u∈X*.
Let S' be the set of words v of the form v=wp with (w,p) good but not very good. Then we define S= P∪S'. Note that P∩S' may be nonempty, and that any element in S' \ P is of the form wp, with (w,p) good but not very good and w∈X+. Moreover, let R be the set of words v of the form v=xwp with x∈X,w∈X*, (xw,p) very good, and wp∈S with (w,p) good. Then Y= X∪RS*, which is a rational code having deciphering delay d containing X.
报告时间：2021年11月21日上午8:30
报告地点：腾讯会议(会议号:972 7906 7171)
邀 请 人：乔虎生教授
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【报告人简介】
曹春华，云南大学bat365在线平台官网登录教授，云南大学青年骨干教师，研究领域是半群代数理论。主持国家自然科学项目2项，主持省科技厅应用基础面上项目2项，主持省教育厅重点项目和一般项目各1项，2019年参与云南省科技厅高端人才引进项目1项，在《Acta Informaitca》《International Journal of Computer Mathematics》等杂志发表科研论文30多篇。主讲的《抽象代数》课程为云南省研究生优质课程。指导全国大学生数学竞赛，2位同学获国家一等奖，1位同学获国家二等奖，5位同学获国家三等奖，30位同学获省级一等奖，100多位同学获省级二、三等奖； 本人获全国首届高校数学微课程教学设计竞赛西南赛区二等奖；指导云南省优秀硕士学位论文1篇。
