In Alice's Adventures in Wonderland, Lewis Carroll famously left a riddle unanswered: Why is a raven like a writing desk?
"Have you guessed the riddle yet?" the Hatter said, turning to Alice again.In a later edition Carroll offered an answer: Because it can produce a few notes, tho they are very flat; and it is nevar put with the wrong end in front! Alas, a humorless copy editor ruined the best part of that joke by changing 'nevar' to 'never' before the edition was published, so the answer was never published as intended.
"No, I give it up," Alice replied. "What's the answer?"
"I haven't the slightest idea," said the Hatter.
"Nor I," said the March Hare.
Alice sighed wearily. "I think you might do something better with the time," she said, "than wasting it in asking riddles that have no answers."
Another excellent answer was offered by 'puzzle maven' Sam Lloyd in 1914 (according to Cecil Adams' The Straight Dope): Because Poe wrote on both.
In my own novel, The Bride Stripped Bare By Her Bachelors, Even, there is a similar unanswered riddle. As the three main characters complete the first half of their road trip from Medford, MA by driving into Philadelphia, PA, one of them, Greg, plays Elton John's song Philadelphia Freedom. He asks the others: For ten points, and today’s grand prize, who can tell me what that song has to do with Duchamp? The chapter ends there; no answer is ever given.
Greg is obsessed with anagrams, for reasons that are partly to do with Duchamp, who greatly enjoyed anagrams and other wordplay. I asked my son to write me an anagram-finding computer program that could deal with long strings, which most on-line anagram tools cannot. There are at least 671 English words contained inside the string Philadelphia Freedom, and my son's program found 296,613 anagrams that used all the letters. I wrote my own computer program to help conduct a systematic search through this set, looking for an anagram that might serve as an answer to Greg's riddle. I found several candidates, but my son and I selected this one as our favorite:
LIMP? HAHA! DID LOPE FREE!Duchamp's life can be seen a celebration of freedom, as a throwing off of all limitations. He never limped along but rather ran freely: i.e. he DID LOPE FREE.
[Image from: http://ellelirie.blogspot.ca/2012_07_01_archive.html]