You and your friend are in Lolitaville in search of Vladimir Nabokov’s recently released and incomplete novel, The Original of Laura, and happen upon two bookstores: R and L. You know without a doubt that the sole copy of Laura in Lolitaville is in one (but only one) of the two bookstores, but are unsure which exactly. You also know that whichever bookstore you enter, your friend will enter the other; which is problematic, because you really want to read the book before s/he does.
Now let us presume the population of Lolitaville consists of exactly two types of people: inveterate liars and uncompromising truthtellers, both of which are utterly indistinguishable from each other. All you know is that liars must lie and truthtellers must tell the truth. Let us further presume that each and every inhabitant- whether liar or truthteller- knows exactly which bookstore has Laura for sale. Now, you must ask a question and time permits you to ask one and only one to one and only one inhabitant. To complicate matters, the question must be polar (i.e. answered by either a ‘yes’ or ‘no’).
Alas! the question: Given the above conditions, what question would you ask in order to know, without a doubt, which bookstore you ought to enter?
P.S. For those with whom I have before discussed this, I challenge you to find another answer besides the one expected above.