CH 73

“Discrete mathematics is a mathematical discipline that studies the structure of discrete quantities and their interrelationships. Discrete mathematics can also be said to be the basic core discipline of computer science as it’s the bridge between mathematics and computer science.”

This was what Xing Conglian had read aloud when he was reading the explanation for “Discrete Mathematics”, and then he was interrupted by Wang Chao.

“I’m familiar with discrete mathematics, Captain. Why do you still need to go to Baidu? Are you looking down on me?”

“Then do tell Mr. Wang, why did Jin Xiaoan look at the ‘Discrete Mathematics’ on the bookshelf when Fu Hao called out ‘Jiang Liu’s’ name?”

“How do you know she’s reading ‘Discrete Mathematics’?! It could also be ‘Everything Starts with an Encounter’ that’s next to it.” Wang Chao responded rhetorically.

“Because in Wang Shishi’s dorm, we also found the same ‘Discrete Mathematics’ book that belonged to Xu Haozhen…”

“What1?” Wang Chao shuddered. “Unbelievable!”

“Speak properly!1” Xing Conglian smacked the boy on the head.

1Clarity: Wang Chao is saying (神马) which is an internet buzzword that’s a homonym for what (什么). The word Wang Chao is using is a reference to a flying god horse (Pegasus). Xing Conglian is telling him not to use slang (also, he says unbelievable in English).

“Shit, ‘Discrete Mathematics’ isn’t advanced mathematics. It’s not a compulsory course at a university. They’re not majoring in mathematics or computer science, right? Why are they suddenly interested in this?”

Listening to the chatter in his ears, Lin Chen lowered his head and looked at Professor Fu, who was chatting awkwardly with Jin Xiaoan on the screen. What they were saying in the conference room was passed through the mic and fell into Fu Hao’s ears, which made Professor Fu’s facial muscles stiff as he didn’t know what to do next.

“Professor Fu… Guess, will Jiang Liu’s name be written on the title page of Jin Xiaoan’s ‘Discrete Mathematics’?” Lin Chen said this through the mic, which caused an obvious shiver from Fu Hao on the screen.

However, the only way to verify the speculation was by hand.

This time, he didn’t tease Fu Hao anymore and said, “Don’t you have that file bag under your armpit? Pretend to read the book ‘Everything Starts with an Encounter’ while holding the cigarette case in your other hand, and then act careless and pull out the ‘Discrete Mathematics’.” When Fu Hao was facing girls, he could only use about 0.1% of his usual speaking ability, so all Lin Chen could do was instruct, “You can say to Jin Xiaoan, ‘You have also read this mystery novel’.”

In short, the instructor’s level wasn’t high either. Fortunately, Fu Hao’s movement had been awkward since the beginning, so whether he was to say this or take his next action of getting the books off the shelf, it wasn’t unexpectedly abrupt.

Several books fell to the ground, and Fu Hao squatted down, blocking Jin Xiaoan’s sight. He first put a certain reasoning book back on the table and then said, “This book is really good. Have you finished reading it?”

Then, pretending, he inadvertently quickly flipped over the book “Discrete Mathematics” and used his other hand to aim the cigarette pack to film the process of him flipping through the entire book in a dedicated manner.

“Is this ‘Discrete Mathematics’ the same as Wang Shishi’s?” Wang Chao manually slowed down the recording on screen and dragged the progress bar forward as he asked.

“The same.” Lin Chen stretched out his finger and gently drew a circle on the screen.

In the lower right corner of the title page, the name “Jiang Liu” was really there.

“Pay attention to the copyright information page and take a picture of it, then you can leave.” After Lin Chen finished speaking, he turned off the microphone.

The conference room was silent. Lin Chen didn’t speak, and neither did Xing Conglian. Even Captain Jiang, who was usually carefree, didn’t dare speak.

Therefore, the only one who still made a peep in this current situation was Wang Chao.

“Is this some kind of sorority where they send each other books and urge them to study hard?”

The teenager’s voice was still light and sweet. Although this question wasn’t too useful, just listening to Wang Chao’s voice made everyone inexplicably relaxed.

“Can you explain a little what Discrete Mathematics is?” Lin Chen asked.

“I can’t explain it to you. The subject is too big, and there’s so much content that it’ll be too difficult for you.” Although this state was equivalent to saying, “You mortal have too low of an IQ”, the sincerity in Wang Chao’s eyes made it hard for people to smack him in the head.

While they were talking, Xing Conglian watched Fu Hao as he read the original Discrete Mathematics seriously and suddenly said, “It’s a bit strange.”

“What?”

“Look, this book is a bit worn, but there are no marks in it…” Xing Conglian pointed to the curled corner of the book and said, “The book that Xu Haozhen gave to Wang Shishi was also in the same condition. Though it looks tattered, there were no obvious notes or writing in the book.”

“What’s wrong with no notes? A normal person can’t stand reading more than 10 pages of this kind of book,” Wang Chao interjected.

At that moment, the little comrade Wang Chao had a flash of inspiration and turned to Lin Chen and said, “A’Chen, the Captain is asking you!”

Lin Chen was amused by this. The original foggy situation suddenly became clear. “Seeing that the book is worn on the edges only proves that it has been flipped through many times, but it can’t prove anything else.”

“Can’t prove what?”

“It can’t prove that either Jin Xiaoan or Wang Shishi had read this book seriously.” Lin Chen glanced at Xing Conglian and continued, “Most people who read professional books like this would take notes while reading it…”

“But it may also be that this book is very precious to them and they’re reluctant to write in it!”

Seeing that Wang Chao was drawing inferences from this, Lin Chen nodded with satisfaction. “That is indeed the case, so now there are two possibilities. The first is that they didn’t read ‘Discrete Mathematics’ seriously and simply just flipped through the book over and over again, so the subject matter that’s in it doesn’t make any sense to them. The second is that they have studied ‘Discrete Mathematics’ seriously only because they cherish this book too much and have not written any notes in it… Which one do you think is more likely?”

Wang Chao scratched his head. “I don’t know! But to be honest, I’m not a math or computer major. It’s too hard to learn Discrete Mathematics. The founders of set theory are crazy…”

“So you agree that it’s the first point?” Lin Chen interrupted the teenager.

“A’Chen, I think everything you say is right!” Wang Chao said this to him shamelessly. “So the answer is that they really don’t understand shit and they are just flipping through the book?”

“Correct.”

“But how do you know?”

“Ah, because you just showed me Jin Xiaoan’s file, which contains her college transcript. She flunked math in high school,” Lin Chen said.

Upon hearing this, little comrade Wang Chao quickly took a breath and then said plaintively, “A’Chen, don’t learn from the Captain. It’s not good…”

“It’s important to be careful in the process of handling cases.” Xing Conglian knocked on Wang Chao’s head and continued, “And there’s nothing to brag about after learning discrete mathematics.”

“But why, ah, are they practicing qigong* or something? Are they flipping through the book to try and reveal its meaning?” Wang Chao asked depressingly.

*A system of coordinated body posture movement, breathing, and meditation used for purposes of health, spirituality, and martial-arts training.

“If you add a few other keywords in this case, such as the ‘dark web’ and ‘drugs’, do you see any association with this?” Xing Conglian continued to ask.

In an instant, Wang Chao’s eyes changed. “Shit Captain, I’m getting the creeps. What’s wrong with you thinking about this kind of stuff at night!”

After the teenager said this, the entire room fell into an unbearable silence.

Lin Chen clenched his right hand and also fell silent.

A tattered book, a group of college students, a controlled group, a dark webcast, drug dealing, a jewelry heist…

If they connected these keywords in a series, it would look something like this: Someone has gained control of a group of college students through various means, not only using them to conduct various webcasts and make huge profits but also involving them in hundreds of millions of dollars’ worth of stolen jewelry and transnational drug-related crimes. The only clue they had in their hands right now was that these students all have a strange ‘Discrete Mathematics’ book.

Then, the role of this book seemed obvious.

“What the hell is going on. I find that you don’t like to explain things in plain words.” Jiang Chao finally couldn’t help but break the tacit silence.

“Let’s put it this way, why did the mastermind behind the scenes use the dark webcast?” Wang Chao asked rhetorically.

“In order to not be found!”

“Yes, whether it’s the onion server or the dark web, it’s essentially a service to protect personal privacy. In other words, it’s an encryption method. Then if someone controls a large group of students, that person needs to give instructions to these kids, so they have to ensure that the information they sent is safe, right?”

“No way. Do you think that book is a code book? What age is it now that you still play with this kind of thing, and we haven’t found this book in the relics of the other deceased.” Jiang Chao reacted quickly, then continued, “And don’t they have the dark web? So wouldn’t it be more convenient to have a dark forum or something to communicate on the internet?”

“Oh, it’s simple. Don’t organizations take back such important things before they die? Are criminal organizations so stupid that they leave such obvious clues for you to investigate? It’s estimated that Wang Shishi’s book must have been destroyed for a special reason! And in fact, although this encryption method is very simple, it’s actually quite effective and elusive. First of all, even if your roommate sees it, few people would actually read a book like ‘Discrete Mathematics’, but if you’re looking at a strange webpage on the internet, that’ll make it look quite suspicious. Things like text messages and WeChat can easily be traced. As for this book, there are many formulas and strange characters. For example, if I report the number 1612, do you know if I’m referring to page 16 line 12 or page 1 line 6 and the 12th word? If that word happens to be a minus sign, do you know if it means backspace, carry, or delete? Of course, in theory, this encryption method can be cracked, but it requires a lot of data and calculation analysis. Therefore, a math book can really be used as an ideal code manual… The reason why I think it’s ideal is because, except for my Captain, who the hell would associate a good book with underground cipher work!”

“I think you’re complimenting me,” Xing Conglian said coldly.

Finally, Team Leader Ren, who had been hiding in the corner, suddenly became interested in this topic. But it wasn’t so much interest in itself but rather his biggest concern was… “You mean, they use this ‘Discrete Mathematics’ as an encrypted manual to transmit information? I think the reason why you can think this is probably because this encryption method is used by underground criminal organization. To be precise, it’s a method that drug dealers love to use, which means I can suspect that these students, in fact, are being used to covertly smuggle drugs?”

“You can suspect this, but such suspicion is basically useless right now,” Xing Conglian said callously.

“You can’t stop my investigation just because of your own case!”

“I seem to have said that everything related to Fang Zhiming’s drug factory case is not in the general direction of our investigation for the time being.”

“This is a major clue. We can follow it!” Ren Xian suddenly raised his voice.

“Oh, then has Team Leader Ren intercepted any codes?” Xing Conglian glared at him, and with this one sentence, he made Ren Xian speechless.

“Not yet, but I can review the file and maybe there will be clues…”

“Well, if you’re lucky enough to intercept a string of passwords, and your conclusion is verifies that someone is manipulating a group of students to carry out countless illegal and criminal activities, including using them to deal drugs, and then, you can use this to catch the mastermind behind the scenes or save these children?” Xing Conglian’s voice was cold. He reached out his hand and pointed to Wang Chao’s laptop. The picture was fixed on the girl in the seat with her head slightly bowed. “You still don’t understand. Is there a difference between this case and the homicides we have encountered before?”

“I…” Ren Xian wanted to say something, but he didn’t understand the problem.

“What’s the difference?” Jiang Chao interjected.

Lin Chen looked at the captain of the criminal division, who was apparently angry at the two, and couldn’t help but pat the back of his hand and explain for him. “The difference is that in ordinary homicides, we only need to find the murderer, but in this case, even finding the person behind this isn’t the most important thing.”

“Isn’t it important to catch the person behind it?”

“Compared with the imminent bloodshed and a group of manipulated college students, the question of who’s behind it and what they are doing with these students isn’t important. How to solve the current crisis is the most important.”

After Lin Chen finished speaking, he looked at Xing Conglian again.

In fact, if he hadn’t explained for him, he would not have discovered that Xing Conglian’s thinking had always been clear and his priorities couldn’t have been more precise.

Quite honestly, it was so correct that Lin Chen had nothing to say.

“Then find the mastermind and stop him from acting. Isn’t this the fastest solution?” Jiang Chao asked again.

“We now have two available clues, a book and a person. Assuming that Discrete Mathematics is really a cipher sheet, right now we haven’t even intercepted any corresponding passwords. This clue is basically useless to us. As for Jin Xiaoan… Didn’t you try to pry open Cheng Weiwei’s mouth that day? Seeing as how Jin Xiaoan is exactly like her, do you think you can get her to open her mouth and extract any useful information?” Lin Chen continued.

Wang Chao raised his hand plaintively and asked, “Then aren’t we still at a dead end right now?”

“Who said that?” Xing Conglian twisted Wang Chao’s ears. “First of all, we can compare Wang Shishi’s Discrete Mathematics to Jiang Liu’s to determine whether they are the same version, and then check the copyright page and find out the publisher to see the print run and outgoing records to find out how many books are out in Yongchuan. Do I need to teach you this kind of thing?”

“I can handle this kind of trivial matter…” Wang Chao patted his chest, and his hands started flying. “First look at the edition!” As he spoke, he enlarged the copyright page picture on the screen, then said, “Congratulations gentlemen, this book is the first printed version in 2001. The print run was 5,000 copies. In other words, it’s really an antique!”

“The good thing about the old edition is that it probably hasn’t been sold online…” The boy clanked on the keyboard and then clicked his tongue. “Bingo, it really hasn’t been sold online. I don’t know how to evaluate your luck, sir.”

“So, is our luck good or bad?” Xing Conglian asked dryly.

“Since it hasn’t been sold online, it means it went through the publisher’s channel. The good thing is I can check the publishing house’s outbound records. The disadvantage is that the time period is too long. It’s very likely that multiple distributors have ordered this book in different batches, and any system can only find the primary distributor, no secondary ones, so…”

The teenager’s voice abruptly trailed off.

Although he made a lot of assumptions, after setting the search criteria and once the search was finished, only one dealer’s name appeared in all of Yongchuan.

[Yongchuan Siyuan Inspirational Book Distribution Co., Ltd. Chang Wei 139XXXXXXXX]

At this moment, Jiang Chao also handed the pictures on his phone to Wang Chao.

The young man glanced at the photo, quickly copied the address of the bookstore, and sent it to his captain. “The two books are the same version. I sent the address to your phone, Captain. You can go now. Bye bye!”

The time was 8:31 in the evening.

Lin Chen first looked at the time displayed on Xing Conglian’s phone, and then looked at the address. He found that the location of the dealer happened to be in the bookstore of University City, so he said, “Phoenix Book Mall usually closes at 9. If we drive a little faster, we should be able to make it.”

Xing Conglian had already turned around and was ready to leave. When he heard what Lin Chen had said, he suddenly turned to Ren Xian. “It’s almost 9 here, which means it’s probably morning in the time zone across the ocean. Please keep an eye on it, Team Leader Ren. If there’s anything on the internet, just tell this kid to do it.” After he finished speaking, he pointed to Wang Chao’s head, then, as if he wasn’t at ease, instructed, “Don’t communicate with those people. If they provide useful information, we’ll pay. This will be the fastest way.”

Kinky Thoughts:

Discrete mathematics is the study of mathematical structures that can be considered “discrete” (in a way analogous to discrete variables, having a bijection with the set of natural numbers) rather than “continuous” (analogously to continuous functions). Objects studied in discrete mathematics include integers, graphs, and statements in logic.

It is the branch of mathematics dealing with objects that can assume only distinct, separated values. The term “discrete mathematics” is therefore used in contrast with “continuous mathematics,” which is the branch of mathematics dealing with objects that can vary smoothly (and which includes, for example, calculus). Whereas discrete objects can often be characterized by integers, continuous objects require real numbers.

The study of how discrete objects combine with one another and the probabilities of various outcomes is known as combinatorics. Other fields of mathematics that are considered to be part of discrete mathematics include graph theory and the theory of computation. Topics in number theory such as congruences and recurrence relations are also considered part of discrete mathematics.

The study of topics in discrete mathematics usually includes the study of algorithms, their implementations, and efficiencies. Discrete mathematics is the mathematical language of computer science, and as such, its importance has increased dramatically in recent decades.