A new puzzle will appear each month.
When you have solved the puzzle, you may submit your solution.
The solution will be given the following month, along with credit to those who have solved the puzzle.
Puzzle #6 for September “Inspector Craig Visits Transylvania”:
Craig of Scotland Yard was called to Transylvania to solve some cases
of vampirism. Arriving there, he found the country inhabited both by
vampires and humans. Vampires always lie and humans always tell the
truth. However, half the inhabitants, both human and vampire, are
insane and totally deluded in their beliefs: all true propositions they
believe false, and all false propositions they believe true. The other
half of the inhabitants is completely sane: all true statements they
know to be true, and all false statements they know to be false. Thus
sane humans and insane vampires make only true statements; insane
humans and sane vampires make only false statements. Inspector Craig
met two sisters, Lucy and Minna. He knew that one was a vampire and one
was a human, but knew nothing about the sanity of either. Here is the
Craig (to Lucy): Tell me about yourselves.
Lucy: We are both insane.
Craig (to Minna): Is that true?
Minna: Of course not!
From this, Craig was able to prove which of the sisters was the vampire. Which one was it?