"Devil's proof" is a proof that is almost impossible to completely deny or affirm in practice.
For example, you probably can not completely deny the possibility that a devil appears as soon as you are convinced that you can prove the absence of a devil.
In fact, the demon appeared in front of me like that. "Wow, it's a devil."
The devil frowns. "You are rude, I am an ordinary human being."
"Huh, prove that you are not a demon." "Please do not overdo it."
"So, what is it for?" "Please return the lent money."
"Wow, you're a demon after all." "When you borrow, you are saying that I am God Buddha."