The five of them lined up and turned back the way they came.

"It's still comfortable to go downhill!" Ke Xin said as he walked.

"Don't talk, pay more attention to the signs we left on the side of the road, Seami walked for three days, and we only walked for less than a day before catching up with them, I always feel that there is something strange in this." Yun Yanuan did not extinguish the torches of several people, and always paid attention to the situation on the cliff.

Kexin stuck out his tongue and grimaced, but he knew that this was not child's play, and he hurriedly focused on the situation on the cliff, for fear of missing the mark.

"Here, here, the last mark we left behind!" Ke Xin pointed to a meter and a half high above the cliff face, a lump of golden snake oil stained with a bright red wildflower.

"Everyone, pay attention, from here on, every few hundred steps, there is a mark, pay attention, don't miss it!" Yun Yanuan reminded.

Sure enough, going down here, it didn't take long for you to see small marks, big or small, and so on all the way down until Kexin found the last mark.

"This is the last one, a few hundred steps down, you will reach the exit, I am really puzzled, how did you walk for three days!" Finding the last mark, the exit was not far away, but Xin breathed a sigh of relief and couldn't help but start to doubt again.

These cliffs are very strange, they are black, and I don't know what kind of material they are, if it weren't for these marks, even if they were lit with torches, the walls would be like a dark night, but unfortunately there was no starlight embellishment.

"The material of this cliff is very strange, it seems to be coated with a layer of light-absorbing material, no matter how much light you hit, there will be no trace of light refracted back, as if it has been completely absorbed, I want to get a piece and go back to study it." Kexin stroked the rock wall and said.

One hundred steps... Two hundred steps... Five hundred steps... A Thousand Steps......

"No, the first mark is only a few hundred steps from the exit, and we've walked more than a thousand steps now!" Kexin had been silently counting her steps, and at this moment she couldn't help but exclaim.

"And when we entered, we didn't find a fork in the road, a road in Huashan, why didn't we go out?" Yun Yanuan said, and couldn't help but feel numb in her back.

This is too weird, there is only one way, but how can this situation occur.

"Yun, should we go back and find the exit!" Diana was a little flustered and said anxiously.

"There is only one way, we go all the way down, but the exit is gone, turning back at this time, to no avail!" Yun Yanuan thought for a while and said.

Instead, he looked back at Kexin and asked, "Kexin, what do you think?" "This girl can always find the crux of the problem, especially this kind of problem that is beyond common sense.

Kexin shook his head vigorously, and said with a depressed face: "I'm in a mess now, I feel like my brain is about to collapse, how can this happen!" We have been going downhill, we should go out directly, but in fact we are not, we are still in Shandong, and we are still drawing circles, how do you let me explain? ”

Maya, the little girl, pinched her arm hard, and murmured the hardest, "We can't be dreaming!" ”

Then he exclaimed, "It hurts, it doesn't look like a dream!" ”

The speaker has no intention, but the listener has the intention, but when the heart hears this, he suddenly cries:

"Hey, no, there seems to be an explanation!" Ke Xin's eyes suddenly lit up, as if she thought of something, she took out one of the lower teeth of Candle Jiuyin in the grass building, and wanted to draw something on the ground, but the ground was very hard, and it was pitch black, and it couldn't be depicted at all!

Yun Yanuan pointed to the snake oil in her straw basket and said, "Use snake oil, it's golden, and your teeth are used as pens." ”

"It's worthy of being a devil six, but there are a lot of ideas!" Ke Xin seemed to have found the reason, and was very excited at the moment, and immediately according to what Yun Yanuan said, snake oil made ink, and began to draw on the ground.

It's a very ordinary drawing, rough but easy to see.

A regular circle pattern, covered with steps, one by one, can be seen that Kexin's sketching skills are good, and this picture looks three-dimensional.

"Maya reminded me, or I forgot about the staircase." Kexin looked at the pattern under his feet and said.

"Me? What did I remind you? Maya asked, puzzled.

"You said dreaming, I remembered that I once saw a similar situation in my idol Xiao Li's movie Inception." Then Kexin pointed to the pattern and asked, "Did you find anything?" ”

"Isn't it just a round ladder? What's so strange? Diana looked at it for a moment and wondered.

Yun Yanuan frowned and looked at it for a long time, but she didn't see anything wrong, this picture was too ordinary, there was nothing strange at all.

It was Ami Se, who looked at it for a while, and suddenly came to her senses: "This is the Penros Ladder?" ”

"Solution!" Kexin snapped his fingers and smiled: "I finally have someone who likes to read to chat with me!" That's right, this is the slightly modified Penrose Ladder. ”

It seems that they don't understand Yun Yanuan, Se Ami is very weak and has no meaning to speak, and Kexin doesn't like others to steal her limelight in this regard, so she didn't sell it this time, and said directly:

"The prototype of the Penrose Staircase is square, I drew it as a circle, the principle has not changed, this Penlos Staircase is famous because it is a false proposition, it is impossible to realize it in 3D space, but on the plane of 2D, it can be displayed in front of people's eyes in a three-dimensional three-dimensional form."

Teacher Kexin began to lecture and looked at the reactions of several people very professionally, but it seemed that the duck listened to the thunder, and couldn't help but be a little angry: "You haven't seen the problem yet, right?" ”

The three ducks shook their heads vigorously.

Ke Xin put his hand on his forehead, his clothes were in pain, and he pointed to the so-called Panloth stairs at his feet and said, "Don't you see that all the steps of this staircase are upward?" ”

Yun Yanuan shrugged his shoulders and said, "Aren't all the stairs like this?" It's either up or down! What's so strange? He felt that Kexin's picture had no meaning at all.

Ke Xin was mad, and said angrily: "Then have you ever seen a ladder that goes all the way up, and finally connects with the bottom ladder to form an infinitely extended circle?" Ever seen it? Ever seen it? ”

The three of them suddenly realized, and Yun Yanuan was surprised: "Damn, this is impossible, this is a visual deception!" Completely contrary to the objective law! The person who invented this picture is really too thoughtful to be a professional liar. ”

Maya also nodded and said, "Yes, this is just something that deceives people's eyes, and it can't be real!" The two ends of the staircase will inevitably produce a distance difference, and it is impossible to connect them in one place, and this phenomenon is absolutely impossible! ”

Ke Xin shook his head and asked, "Then do you think that the cave we are in is very similar to this Penros Staircase, whether you keep going up or going down like now, but there seems to be no end......