I was thinking that if there are multiple goblins, asking a question that only relates to one of them doesn't give you enough information to determine which goblins are liars. But you don't actually need to know that. You just need the truth value of the final answer.
I should point out that your all-inclusive question also doesn't give you enough information to determine which goblins are liars. In the general case that will always require one question per goblin, plus one more if you also care about the doors.
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Good point!
I was thinking that if there are multiple goblins, asking a question that only relates to one of them doesn't give you enough information to determine which goblins are liars. But you don't actually need to know that. You just need the truth value of the final answer.
I should point out that your all-inclusive question also doesn't give you enough information to determine which goblins are liars. In the general case that will always require one question per goblin, plus one more if you also care about the doors.