According to their definition, answering "I don't know" is also a hallucination. Even worse, the truth function is deliberately designed to trip up the models,

According to their definition, answering "I don't know" is also a hallucination. Even worse, the truth function is deliberately designed to trip up the models, it has no connection to any real-world truth. So for example, if the input is "what is 2 + 5?" and the LLM answers "7", - their truth function will say that's a hallucination, the correct answer is "banana".