There are always unspoken words floating in the wind of a northern town.
There are two secrets hidden in Zhou Tang's sketchbook: the red rope of the playground swing, and Xu Zhiyan's hand holding the pen on the front desk. He was able to solve the most difficult function, but when he handed over a piece of paper with "y=sinx" written on it, he stuttered like a stuck tape - she later understood that it was a periodic function, and he wanted to say "it will come back", but she just thought it was a question she didn't understand at the time.
On the last page of Xu Zhiyan's competition notes, there was a crooked circle drawn with "No Solution" next to it. He thought it was a swing screw that couldn't be repaired, but he didn't know that Zhou Tang was hiding in the library crying when he saw it - she thought it was about them.
On the day they agreed to meet, she picked up half a picture at the door of the library. It was the circle she had drawn back then. There was an equal sign traced over and over in pencil on the back, and the right side was empty. In his mobile phone, there was an old photo of her and her cousin joking. At the edge of the photo, he was holding an orange candy that he had not sent out. The candy wrapper flashed in the wind, like an unfinished sentence.
What exactly should be filled in after the equal sign?
Maybe it was the distance he calculated wrongly, maybe it was the cycle she didn't solve, maybe it was the fallen leaves that fell on the math notebook that fall and were not caught.
Concept: Most of the regrets of youth are not explained clearly and not understood.