25: Chapter 25 The First Lesson of University in a Fifteen-Square-Meter Space

Accompanied by that familiar sense of weightlessness, his vision refocused from a brief blur.

Beneath his feet was the familiar dark red hard soil.

Not far away, that two-hundred-square-meter farmland lay quietly under the dim light.

The withered stems of the potato seedlings still stubbornly stood upright in the ground, and even the angle of their lodging was identical to his memory.

In the small area next to it, the traces of Soybean straw being turned into the dark red compacted soil were still fresh, as if he had just put down the entrenching shovel the previous second.

Farther away, under that heavily weathered, huge concrete load-bearing wall, a small patch of grayish-green Moss representing the miracle of life in the dried riverbed curled up in the shadow of the rock eaves.

Everything remained completely unchanged.

Time in the Wasteland was completely frozen during the days of his absence.

Only when he stood here would the gears of this planet begin to slowly mesh again.

Jiang Lin took a deep breath and unloaded the supply pack on his body.

Looking at the solar panel groups, storage batteries, inverters stuffed to the brim in the supply pack, and those moisture-proof boxes full of knowledge, and then looking up at the Stone House in front of him that was only four square meters, Jiang Lin scratched his messy hair and let out a long sigh.

"Too hasty."

What was the concept of four square meters?

Two meters each in length and width.

During the first three trips to the Wasteland, this place was a life-saving dog hole for him; with a sleeping bag spread out and some potatoes, Soybean, Pumpkin, and vegetable leaves piled up next to it, he could get by.

But the things he brought this time were different.

If several huge solar storage batteries were moved inside and a proper desk was set up, this four-square-meter space wouldn't even have room to turn around.

Locking a person in a coffin-like box for more than ten years, without waiting for Advanced Mathematics to drive him crazy, claustrophobia could deprive him of his sanity first.

A depressive environment was definitely not conducive to studying.

"Sharpening the knife does not delay the work of woodcutting." Jiang Lin thought about it and covered the newly taken out supplies with a rainproof cloth.

Picking up a newly brought-in entrenching shovel, he strode toward the heavily weathered concrete building ruins on the west side of the camp.

First priority change: construction and expansion.

For the next ten full days, time in the Wasteland completely turned into Jiang Lin's personal infrastructure channel.

He first dismantled the originally south-facing wall of the Stone House, and then extended outward based on that.

Physical labor was very boring and also grinding.

Jiang Lin was like an untiring ant, traveling back and forth between the ruins and the camp every day.

He pried out those concrete fragments weathered and peeled off by time, picking up large pieces of Gobi rocks.

He couldn't move stones that were too heavy, so he used the principle of leverage, placing round logs underneath, and stubbornly rolled them back bit by bit.

New blisters were rubbed out in the web of his hands, and after the blisters broke, they turned into calluses.

On the evening of the eleventh day, the project finally came to an end.

Jiang Lin stood in front of the completed building, wiped the mud and sweat from his forehead, and his heart was full of a sense of achievement.

The originally cramped four-square-meter dog hole had been expanded by him to fifteen square meters.

He horizontally framed a dozen thick steel bars pulled out from the ruins on the roof, covered them with flat stone slabs, padded a layer of waterproof cloth, and finally plastered them with red mud mixed with withered grass.

To prevent water leakage, he specially made the roof into a certain inclination angle.

Pushing open the crude wooden door pieced together with a few waste wooden boards, the space inside suddenly opened up.

Fifteen square meters were clearly divided into three functional areas by him.

The innermost corner against the wall was the living area, about 4 square meters, paved with moisture-proof mats and sleeping bags, with pottery jars filled with potatoes and clean water placed next to it.

The side close to the door was the energy and storage area, specially used to place battery packs, inverters, and various sundries.

And the largest area, a full seven square meters, directly faced a small square window he specially left on the south wall.

This was his Wasteland study.

Jiang Lin used two thick square concrete pillars as legs, and on top of them framed a stone slab he carefully selected and found in the ruins.

The stone slab was somewhat incomplete, and the edges still bore traces of snapped steel bars, but as a desk, it was broad and steady, full of rugged beauty.

Jiang Lin walked to this broad stone desk, reached out and patted the cold stone surface, kicking up a little fine dust.

The space became spacious, and the cramped feeling pressing on his heart was swept away.

The wind of the Wasteland poured in from the small square window, carrying the dry breath unique to the Wasteland.

Jiang Lin nodded in satisfaction, turned around and walked out of the Stone House, carrying in the sparks of civilization wrapped layer by layer in moisture-proof bags one by one.

Hard drive No. 1 was packed with all teaching videos, courseware, and PDF textbooks of Advanced Mathematics and Linear Algebra.

Hard drive No. 2 was General Physics, hard drive No. 3 was English materials and literature, hard drive No. 4 was advanced course backups for junior and senior years, and hard drive No. 5 was various messy reference books and backup systems.

He neatly stacked the hard drives in a plastic waterproof box on the innermost side of the stone desk, with the main laptop placed next to it.

Then, he placed a stack of things in the most prominent position on the stone desk.

At the very bottom were the newly bought Records of the Grand Historian and Tang Poetry, Song Lyrics, and Yuan Operas.

In the middle was Da Liu's The Three-Body Problem trilogy.

At the very top was a small photo album packed in a transparent plastic-sealed bag, containing photos of his parents, a group photo of Class 4, Senior Year of Jiangcheng No. 7 High School, and even a street view photo of a bustling intersection in Jiangcheng.

Looking at the fine wrinkles at the corners of his mother's eyes in the photo, Jiang Lin gently stroked it with his thumb through the plastic-sealed bag.

The Wasteland was a huge silencer and a cruel grinding machine.

Staying here for a long time, people's memories would fade, and human nature would be ground askew by that grand sense of desolation.

He had to put these things in a place he could see as soon as he opened his eyes every day, serving as an anchor to remind himself.

He was not a monster grown out of this red land; he was a person with a place of origin.

Pulling out a piece of the sealed LCD erasable board, he hung it on one side of the inner wall of the Stone House to use for drafting.

The E-ink screen reader was placed close at hand to do semi-formal derivations.

Finally, there was the most critical step.

Jiang Lin climbed onto the rock on the south side of the Stone House, unfolded a foldable monocrystalline silicon solar panel, adjusted the angle of the panel, and ensured that it could catch the dim red sun with the maximum area.

Subsequently, he pulled the thick black power cord along the gap of the Stone House, plugged it into the MPPT charge controller, and then connected it to the lithium iron phosphate storage battery.

Finally, he connected the inverter.

The sunlight of the Wasteland penetrated the clouds and shone on the solar panel.

Fifteen minutes later, the controller's screen flickered.

Following that, a soft beep sounded exceptionally pleasant in this world where there was only the sound of wind.

The indicator light of the storage battery lit up.

First was red representing low power.

After a few hours, it turned into orange representing charging.

In the evening, the indicator light jumped into a vibrant green.

Jiang Lin took a deep breath and reached out to press the power button of the laptop.

The fan made a faint buzzing sound, the screen lit up, and the blue-white backlight instantly illuminated this dim Stone House.

Outside was the dark red Wasteland, the acid rain that would descend again at some unknown time, the weathered and peeled-off load-bearing walls, and a piece of dead despair.

Inside was the glowing screen, the crystallization of human wisdom in the hard drive, paper and pen, and a person preparing to fight against time.

The spark of civilization was re-ignited in this fifteen-square-meter Stone House in the form of 220V alternating current.

Jiang Lin took out the Fourth Wasteland Study Outline and pasted it on the stone wall directly above the computer with tape.

At the very top was that line of bolded large characters.

[Stay as long as you can, study as long as you can.]

Below were densely packed progress bars: Advanced Mathematics, Linear Algebra, General Physics, C language basics...

Everything was ready.

Survival mode ended, knowledge seclusion mode officially began.

Jiang Lin rubbed his hands and drove all the impetuosity brought from the Real World out of his mind.

Clicked on Hard Drive No. 01, and double-clicked to open a folder named 01_01_Advanced Mathematics A (Functions, Limits, and Single Variable Calculus).

As a top student who scored a full 150 points in mathematics in the Senior Year city mock exam, Jiang Lin actually had some confidence in his heart.

He had already beaten high school mathematics.

Derivatives, conic sections, polar coordinates, those things that used to give him a headache, now became the handiest weapons in his hands.

He naturally thought that Advanced Mathematics was nothing more than an extension of high school derivatives and integrals, just pushing down along the way, at worst the formula would be a bit more complicated and the amount of calculation a bit larger.

With a high school foundation of a full 150 points, plus plenty of time in the Wasteland, wouldn't taking down a freshman Advanced Mathematics course be as easy as pie?

He confidently clicked on the video of the first lecture, and at the same time opened the textbook PDF on the left screen.

[Chapter 1: Functions and Limits]

[Section 1: Limits of Sequences]

The old professor in the video had graying hair, wrote a line of words leisurely on the blackboard, and then turned around, saying in an unremarkable tone.

"Classmates, when you reach university, our methods of studying mathematics will change a bit. Let's first look at the strict definition of limits..."

Jiang Lin cast his gaze on the PDF textbook, his sight falling on that definition known as the ε-N language.

[Let Xn be a sequence. If there exists a constant a, for any given positive number (no matter how small it is), there always exists a positive integer N such that when n > N, the inequality |Xn - a| < ε holds true, then the constant a is called the limit of the sequence Xn...]

Jiang Lin scanned this passage of words once.

Didn't understand.

He frowned slightly.

Doing problems in high school had formed a habit of reading ten lines at a glance; maybe he read too fast.

He straightened his body, put away the last trace of perfunctoriness, and re-read word for word.

Any given positive number ε...

There always exists a positive integer N...

Such that when n > N...

Looking at every Chinese character alone, he knew them.

Looking at every mathematical symbol alone, including the Greek letter ε that looked like a backward 3, he also knew how to read it.

But when these things were combined together according to such a weird logical relationship, a brief blank suddenly appeared in his brain.

Of course Jiang Lin did not admit defeat.

He first copied the definition once.

After copying, he circled several words among them: arbitrary, existence, sufficiently large, all hold.

During the third review period, he rarely stared blankly at a definition like this.

In high school problems, definitions were more like labels in a toolkit: derivative was the tangent slope, integral was the area, sequence had a general term, function had a graph.

Knowing roughly what it was, he could continue doing problems.

But it didn't work here.

Every word here was like a screw; turning one less circle, the whole sentence would fall apart.

He tried to take the simplest sequence: 1, 1/2, 1/3, 1/4...

He knew the limit of this sequence was 0.

This was what intuition told him.

But the textbook didn't want intuition.

The textbook wanted him to prove: no matter how small an ε others gave, he could find an N such that all subsequent terms were less than ε.

Jiang Lin stared at that line of words, a feeling of helplessness surging into his heart.

He clearly knew the answer.

But he didn't know how to turn "I know" into "I can prove".

"What is called arbitrarily given?"

"Is this ε a specific value, or a quantity that is always changing?"

"Why give ε first, and then look for N? Why can't this logical order be reversed?"

Jiang Lin picked up a pen, trying to draw a function graph on the LCD erasable board to assist comprehension, just like he often did when doing derivative big problems in high school.

But he got stuck halfway through drawing.

Because he found that drawing could not explain words with strong logical nesting relationships like arbitrary and always exists.

He dragged the progress bar back and listened to the old professor's explanation again.

The old professor drew two parallel dashed lines on the blackboard, forming a strip, and said: "As long as n is large enough, the subsequent terms will all fall within this strip and cannot run out. No matter how narrow you draw your strip, I can always find a starting point N..."

Jiang Lin understood a little; that feeling was like seeing the outline of a building in heavy fog.

He immediately opened the next page of the textbook.

[Limit of a function: ε-δ (Epsilon-Delta) definition]

[...For any given positive number ε, there always exists a positive number δ such that when 0 < |x - x0| < δ, the corresponding function value satisfies |f(x) - A| < ε...]

There was one more Greek letter δ.

The fog closed in again, and it was thicker than before.

The logical outline that had just been established instantly collapsed, smashing him dizzy.

Jiang Lin's fingers hovered over the touchpad, stopping for a long, long time.

It was just the distance of a page of paper, merely the first page of the main text of Advanced Mathematics.

Without any complex calculations, without the eighteen-turn skill traps in high school climax problems.

Only a few lines of purely definitional text.

But it was precisely these few lines of text that crushed his proud self-confidence of 150 points in high school mathematics to pieces.

He suddenly realized a terrifying fact.

High school mathematics and university mathematics might not even be the same species at all.

No matter how difficult high school mathematics was, most of the time it was still about finding a way within established rules.

While university mathematics put the rules themselves in front of him on the first day, asking him: By what right does this path exist?

High school teaches you how to use tools.

University asks you, what is the essence of this tool?

The first day, a whole night, four hours.

His progress stayed on the first three pages.

Jiang Lin irritably grabbed his hair, rubbing his long hair like a chicken nest.

There was a strong impulse to skip these few pages and directly study the derivation formulas behind.

As long as there were formulas, he could immediately do problems, and immediately regain that sense of security of "I am making progress."

But staring at the Study Outline on the wall, he took a few deep breaths and suppressed this impulse.

He did not continue clicking on the video.

That way of comforting oneself with the progress bar had no meaning here.

Jiang Lin turned off the video and flipped the textbook back to the first page.

He wrote four words again on the LCD board.

[Tackle the definition first.]

Below he wrote another four lines.

First, copy the definition three times.

Second, give examples for every quantity.

Third, must prove a simplest example by oneself.

Fourth, do not jump forward if you don't understand.

After writing, he stared at the first line for a long time, and added another sentence beside it.

[University is not about grinding problems, it's about rebuilding the brain.]

This sentence made him a bit uncomfortable.

Because it meant that the clumsy method in the Wasteland that once allowed him to turn things around had to be upgraded here.

In the past, he just did more problems than others.

Starting from today, he must fail more than others, look back more, and dismantle and reinstall those things in his mind that he took for granted.

When reclaiming and farming on the Wasteland for the first time, the red land there was as compacted as stone.

He chopped down with a shovel, the web of his hand numbed from the shock, and only pried open five centimeters of soil skin.

At that time he had also been irritable.

But he shoveled by shovel, spending more than a month, stubbornly turning that piece of land ripe.

"Mathematics is also land."

Jiang Lin said to himself in a low voice, casting his gaze once again onto the pile of ε-δ language on the screen that made him panic with strangeness.