Ramsey's theory is named after the English mathematician and philosopher Frank P Ramsey. It is a branch of mathematics devoted to the study of the conditions under which order must appear. The question in Ramsey's theory usually asks a formal question: "How many elements must be in a particular structure to ensure that a particular property can be held".

The core of Ramsey's theory can be summarized as follows: complete disorder is impossible. From the initial Ramsey theorem to many Ramsey-type theorems developed later, it is shown that as long as the number of elements in the set reaches a certain critical value, a certain property or structure defined by us will definitely appear.

Ramsey theorem of combinatorial mathematics

In combinatorial mathematics, Ramsey theorem, also known as Ramsey's second coloring theorem, is to solve the following problems: how to find such a minimum number? n，make？ n？ Someone must have one? k？ Personal acquaintance or something? k？ Personally, I don't know.

This theorem is named after frank ramsey. 1930, he proved that r (3,3) = 6 in A Problem in Formal Logic. At least three of the six people know each other or don't know each other.

This theorem is equivalent to proving that there is at least one red triangle or blue triangle when the edges of the complete graph of these six vertices are arbitrarily colored with red and blue colors.