"Bayes' Formula"
When Jiang Weilou was sixteen years old, he did what all mathematics students would do - he drew a flower on the back of his answer sheet.
Hua Yuan Ji Shupan took a photo, saved it in his mobile phone, and set it as a private album. In class the next day, the young math teacher leaned on the podium and knocked on the chalk three times without looking back: "Classmate Jiang Weilou, please explain to the class what an impossible event is."
"Impossible events - for example, I got 140 in my math test."
"What about the inevitable?"
"It must be Teacher Ji who wants me to answer questions again."
The whole class burst into laughter. She thought she had won this round until she was stopped by him in the corridor after school. He took out a piece of scratch paper from his shirt pocket - a drawing of a pig's head, with the word "Ji" written not cleanly next to it.
"Jiang Weilou," he pushed up his silver-framed glasses, the corners of his mouth curved meaningfully, "you will become a very interesting adult in the future."
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Later, in the second and third years of high school, there were countless pig heads, white rabbit toffee and probability questions. When he corrected her homework, he never only wrote down the scores, but also had comments next to each wrong question; she threw snowballs at him in the snowball fight when he was surrounded by boys, and gave him a ride when the rear tire of his bicycle had a flat tire. He said she was not a case, but a variable; she said, Teacher Ji, don't wear a white shirt next time. I will draw you once you wear it.
But then, there were seven years of lost contact. He moved away, took the college entrance examination, graduated from college, and started working. She lived the life he expected most - she finished reading the "Theory of Probability" he left for her, and passed the sixty-five he wrote on the bottom of the enamel cup, but she never met another person who would turn around and wave to her at the classroom door.
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When she was twenty-three years old, she was arranged by her mother to go on a blind date.
She opened the door of a western restaurant in the city center and saw a man wearing a dark gray shirt. The silver-framed glasses had been changed to a different pair, but the style was almost the same as seven years ago. The sleeves were rolled up to reveal his well-joined wrists.
When he saw her, the cup he was holding stopped mid-empty.
"... Jiang Weilou."
"Teacher Ji."
He took out a piece of yellowed draft paper from his pocket and unfolded it. On it were her sixteen-year-old round handwriting. He answered this question in front of the whole class back then - the answer was not targeting, but caring.
"You can change it now," he looked at her, his voice quiet and conclusive, like a proposition that had been pushed for seven years and finally proven, "it's not love. It's preference."
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Bayes' theorem says: Update beliefs about original hypotheses based on new evidence.
She once thought that the relationship between them was a small-probability incident, and he once hid all his care in the words "head teacher." But on the day they reunited, he pulled out the Riemann function key she had worn on her eighteenth birthday from around his neck - he made two of them, one for her and one for himself, which he kept for seven full years.
She asked: "Why didn't you come to me then?"
He said: "I am waiting for a condition - when you are no longer my student, when I no longer have to make a risk assessment on my identity."
In the last row of the old classroom, he pulled her into his arms and placed a long overdue kiss on her forehead.
"What now?"
"Now you are the independent variable."
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Lecturer in the Department of Mathematics × Biomedical Engineer | Teacher and student | Five years age difference | From school uniform to wedding dress
"The most fascinating thing about probability theory is that it doesn't guarantee anything. But after getting to know you, I am willing to believe in all small-probability events."
——Ji Shupan
Intention: Love will eventually come