五千年(敝帚自珍)

主题:来个好玩的吧 -- 长颈鹿

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家园 来个好玩的吧

最近吵架太多,俺都不敢来了,今天看见吵得更厉害了,怕怕。

不过呢,在老虎的帖子里看到个牛人

万里风中虎:小议消费需求

凯恩斯主义的宏观经济学在80年代已经破产。原因是出现了比他更了不起的经济理论。凯恩斯以前在剑桥曾经帮助过一个叫Frank P. Ramsey(外链出处)的人。也就是这个Ramsey在20来岁时写的三篇论文,彻底结束了凯恩斯的时代。

应该说,俺有点八卦,特别是对牛人感兴趣

怎么看怎么觉得这个人面熟,点开链接一看,熟人啊

Work

In 1927 Ramsey published the influential article Facts and Propositions, in which he proposed what is sometimes described as a redundancy theory of truth.

One of the theorems proved by Ramsey in his 1930 paper On a problem of formal logic now bears his name (Ramsey's theorem). While this theorem is the work Ramsey is probably best remembered for, he only proved it in passing, as a minor lemma along the way to his true goal in the paper, solving a special case of the decision problem for first-order logic. As it happened, the lemma was not actually necessary for the results he obtained from it. However, Alonzo Church would go on to show that the general case of the problem Ramsey was tackling is unsolvable (see Church's theorem), while, ironically, a great amount of later work in mathematics was fruitfully developed out of the ostensibly minor lemma, which turned out to be an important early result in combinatorics, supporting the idea that within some sufficiently large systems, however disordered, there must be some order. So fruitful, in fact, was Ramsey's theorem that today there is an entire branch of mathematics, known as Ramsey theory, which is dedicated to studying similar results.

His philosophical works included Universals (1925), Facts and propositions (1927), Universals of law and of fact (1928), Knowledge (1929), Theories (1929), and General propositions and causality (1929). Wittgenstein mentions him in the introduction to his Philosophical Investigations as an influence (but not as great an influence as Piero Sraffa).

学过组合数学的都知道拉姆塞(拉姆齐)定理外链出处

或者参加过奥数的肯定知道这个题——任意6个人中至少存在3个人相互认识或者相互不认识

用组合数学的语言就是

在一个K6的完全图内,每边涂上红或蓝色,必然有一个红色的三角形或蓝色的三角形。

(严格的说应该是“如果必然有一个红色的三角形或蓝色的三角形,至少需要完全图的顶点数为6)

用ramsey的语言就是R(3,3)等于6

K5是可以不存在同色三角形的

点看全图

外链图片需谨慎,可能会被源头改

ramsey数的求解是非常难的题,有个八卦故事是erdos说的

“想像有队外星人军队在地球降落,要求取得R(5,5)的值,否则便会毁灭地球。在这个情况,我们应该集中所有电脑和数学家尝试去找这个数值。若它们要求的是R(6,6)的值,我们要尝试毁灭这班外星人了。”

愿意动脑筋的同学可以试试看这个——任意18个人中至少存在4个人相互认识或者相互不认识

就是R(4,4)等于18

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