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The problem was posed by Zheng Jian.
So, Zheng Jian knew very well what the thirty-ninth problem was.
The thirty-ninth problem was an unsolved mystery of the world, to which no one had been able to find an answer or proof yet. 523
The Riemann Hypothesis.
Zheng Jian had included this problem as the thirty-ninth question merely on a whim, and he never thought anyone would be able to solve it while taking his test.
However, he was indeed very interested in the problem.
He had spent several months attempting to find some leads within it.
But.
After several months, Zheng Jian had failed to find any approach to solve the problem, and the endeavor only increased his feeling of pressure.
Because of his obsession, Zheng Jian's overall state was extremely poor during that period.
Ultimately, Zheng Jian had no choice but to give up on finding leads for the Riemann Hypothesis and adjust his mental state.