Find it, wake it up.
Yu Liang formulated a basic problem-solving strategy in his mind.
This is a dream, so the seemingly impossible conjecture of the mathematician could be realized, and he had successfully proven his conjecture in this dream.
Therefore, the best way to break this seemingly illogical conjecture is to shatter his dream.
Awakening character charm.
If you could use the "awakening" character charm on the mathematician, maybe you could send him directly out of the dream and thereby break his mathematical conjecture.
It would then disappear.
So far, it's the only subject to appear in this tale, so if the awakening character charm was to be used, it would be the only target.
Anyway, the ideal first step would be to try to wake it up.
After all, the "awakening" character charm is not that rare, for him, it's only a matter of ordering an extra raw meat meal.