The love of functions and derivatives

Since the high school mathematics text world is created by completely recreating the world of modern human big cities, in this era of advanced technology, big cities at night are usually bright and shining cities that never sleep.

When turning a corner, a figure wearing a black peaked cap on a motorcycle appeared in the car rearview mirror. Function only felt that this figure was familiar, but he didn't think much about it.

The derivative parked the car in the parking lot, and the two got out of the car.At this time, there is still some distance from the building in the community where Function lives.He and the derivative walked and talked.It only rained in the afternoon, and the bright places on the ground are also puddles, and the dark places are also puddles.I avoided the bright one but stepped into the black one. Fortunately, I was wearing sandals, so it didn’t matter if I stepped on a puddle.

Function was still chatting with the derivative without saying a word. In order to avoid the puddle, he lowered his head and moved forward. A distorted black shadow flickered on a bright puddle, peeping at him like a ghost. Function Take a closer look, it is the shadow of a tree.Even though there was no wind, the small bushes trembled.

Function feels a little uneasy.

"Okay, I'll take you here." The derivative shook his hand, "Goodbye."

According to the habit of derivatives, he will stand downstairs, wait until the function walks into his house and turn on the lights before leaving, but these functions do not know.He thought that as long as he walked into this building, the derivative would say goodbye.

A gust of wind blew, and the leaves made a rustling sound, like the wailing of a wronged soul. The water surface shook violently due to the summer wind, and the shadows of the trees were broken into pieces. The shadows on the ground played with their deformed bodies, as if they were about to wrap themselves pedestrian's ankle.

For some unknown reason, Function grabbed Derivative's arm with his hand, and said to Derivative, "...it's so cold, go to my house and have a cup of hot tea before leaving."

The hand grasping his arm was very strong, Derivative looked at the function, and seemed to perceive something from the other's expression: "...Okay."

The function is always holding the derivative's arm, from entering the elevator to getting out of the elevator, and then striding towards the door of his house, taking out the key to unlock it.The whole action of the function is completed in one go, and there is no unnecessary detail to waste time.

The two entered the door immediately, and the derivative watched as the door of Function's house was closed.

Function's tense nerves finally relaxed at this moment, let go of the hand holding Derivative's arm, and exhaled: "I hope it's my illusion."

The oppressive force on the arm suddenly disappeared, but at this moment the derivative didn't have time to recollect, but asked: "What's wrong?"

"I feel like someone is following us."