189.

Although there are many problems on the 2990 floor in front of him, some of which are also very difficult, and some of which he has never seen before, Cheng Li finally relied on a flash of inspiration in his mind to finally solve the problem.

But among the more than 2,000 questions, Cheng Li has never had a question that makes him feel so tricky.

This problem on the 2991st floor is the four-color problem.

"Ask, how can it be proven that any map with only four colors can paint countries with common borders in different colors. ”

The description of the problem is simple and clear, in fact, without causing confusion, a map only needs 4 color markers, so that any two adjacent countries can be different colors.

The problem description is simple, but how to prove this conclusion is very difficult.

The four-color problem, in fact, is one of the three major mathematical problems on the earth in modern times, and it was first proposed by a British college student named Guthry in 1852.

At that time, when he was working on map coloring at a scientific research institute, he found that only 4 colors were needed for each map.

When he discovered this phenomenon, he wondered, can it be mathematically rigorously proven?

This is a typical process of discovering a phenomenon first and then trying to prove it mathematically.

However, when he and his brother tried to prove this four-color phenomenon, they realized that it was a super difficult problem.

Eventually, his brother consulted the famous mathematician Sir Hamilton, but the problem remained unresolved until Sir Hamilton's death.

Finally, the four-color problem has gradually become a problem of concern to the world's mathematical community, and many first-class mathematicians in the world have participated in the four-color conjecture conference.

At first, people thought it was just a simple question.

But except for Kemp, at the end of the 19th century, he proved the five-color theorem and proved that the coloring of a map only needs to use five colors.

But whether the four colors are enough is still an open question.

Until a century has passed, this problem has still not been resolved.

Only then did people realize that this seemingly simple problem was a huge problem comparable to Fermat's conjecture.

For more than 100 years, although the four-color problem has not been solved, the efforts of mathematicians to study the four-color problem have not been in vain.

In order to solve the problem of four colors, the concepts and methods introduced have stimulated the growth and development of topology and graph theory.

In the process of researching the "four-color problem", many new mathematical theories have been produced, and many mathematical calculation skills have also been developed. For example, the problem of map coloring is transformed into a graph theory problem, which enriches the content of graph theory and plays a role in the design of computer coding programs.

Finally, in 1969, after the rapid development of electronic computer technology, people began to try to solve this problem with the help of computers.

For the first time, the German mathematician Hiss proposed a concrete and feasible algorithm for finding the inevitable reduction graph, which he called the "discharge algorithm".

Finally, this problem was finally solved by optimizing the discharge algorithm and performing a large number of calculations by computers.

They carried out tens of billions of calculations, calculated for 1,200 hours on various computers at that time, and modified the calculation program more than 500 times, before finally finding a set of "inevitable approximate graphs".

However, because of the large amount of calculations, it is difficult for human beings to verify whether the calculation process of the computer is correct.

Moreover, the computer proves that although tens of billions of judgments have been made, it is only a huge number of successes, which does not conform to the mathematical rigorous logical proof system, so there are still many people who do not think that the four-color theorem has been solved.

"One of the main problems is that I can't use an algorithm right now, so I can't solve problems with this method that relies on a lot of computing power. Cheng Li said with a headache.

According to the rules of arithmetic tablets, no foreign objects are allowed to be used in the whole process of answering questions.

If Cheng Li is now in the Yuan Infant stage, then he can completely control Jin Dan through Yuan Ying and let Jin Dan assist in calculation, so that as long as he can design that "discharge algorithm", this problem can be easily solved.

However, Cheng Li was only a minor cultivator in the Qi refining stage now, and it was obvious that he couldn't use this method.

"So, in other words, I have to think about it from the beginning, how can I prove the four-color theorem with a concise logical proof process?"

Before his crossing, no one on the earth could prove the four-color theorem by logical proofs, rather than relying on computer heaps to calculate quantities.

If someone can do this, it will definitely make a global sensation.

Cheng Li is tantamount to doing something that no one on earth can do.

The problems of the previous 2990 layer are all problems that have been solved on the earth, even if Cheng Li does not know the specific problem, he will at least have a concept of direction, so as to get twice the result with half the effort.

But now, Cheng Li is tantamount to creating a field that no one has reached before, and the difficulty can be imagined.

"Fortunately, it is not necessary to solve it in the dark from a completely blank state. ”

"At least before that, someone had already proved the five-color theorem, but the one who proved the five-color theorem used the method of counterproof, trying to prove the four-color theorem by looking for an inevitable ductile diagram.

But this method will inevitably produce a huge amount of computation, so this method can only be ruled out. ”

"So what other methods can be used?" Cheng Li fell into deep thought.

As the time passed minute by minute, after 10 minutes, Cheng Li looked up at the time and became a little anxious.

It's 7:30 a.m. on June 14.

"The battle on Qingling Island should have started for a while...... I don't know how the situation is, but the battle must be fierce...... It is estimated that many people have died...... Even if they are old, Lin Meow, and Fang Xiaochun, they don't know how they are doing now, are they okay?"

"No, I can't go on like this, I have to hurry. ”

After thinking so in his heart, Cheng Li took a deep breath and tried to calm himself down.

He knows that the more anxious he is, the more he needs to be calm.

After he calmed his brain down, he thought about the solution again.

"Why don't you try topology to prove it?" Cheng Li finally thought.

"The essence of the four-color problem is the inherent property of the two-dimensional plane, and it is an objective law of the two-dimensional plane. That is, two straight lines that cannot cross in the plane without a common point. ”

"If we follow this line of thought and evolve the four-color problem into a topological problem, we can avoid the large amount of computation required by the counter-proof method, and then the rest is a topological thing. ”