Final? update:

Back in March 2009, I got a note from Eric Mersmann noting that Coudal quietly fixed the puzzle along the lines mentioned below in the “What went wrong” section. (Eric is the “Most-Frustrated Puzzle Player” listed on Coudal's Let's Do Lunch page.)

Update:

Michele wrote today (21 December 2007) to say that they've had a lot of work for clients come in over the past few weeks, so she didn't have time to work on the puzzles;— but that a fix for Let's Do Lunch is coming soon.

Introduction.

Coudal Partners is an advertising and design firm in Chicago. About eight people work for the firm, but I don't know when they can find time to do work for clients, because their amazing web site must demand a lot of their time. I've wasted many an hour watching the short films they make and following their links to interesting Flickr collections and essays about typography.

Occasionally they will publish a logic puzzle. You know the type: You're told that the Dutchman grows lemons and lives next door to the man who drives a Bugatti, and that a Buick is parked next door to the house with a fig tree, and you're supposed to figure out whether or not the New Zealander drives a DeLorean and who lives in the house with the blackberry patch.

This is all harmless fun. But unfortunately, there's a mistake in the puzzle they posted in November 2007, “Let's Do Lunch”.

The Coudal Partners site is so good that an error like this really stands out. As a math nerd, I'd like to think that my fellow nerds in the design and typography worlds would want to fix something like this — it seems to me that anyone who is detail-oriented enough to care about kerning shouldn't be able to stand having a logical error in their puzzle.

I've written to Michele Seiler, the person in charge of the Coudal Partners puzzle pages, but I haven't gotten a response. I don't know whether this is because she's on vacation, or busy doing work for clients, or just sick of people complaining about the damn puzzles, already. [Answer: Busy. See update above.] So the purpose of this site is to provide a record of the details of the problem with the puzzle. I hope that Michele, or someone at Coudal Partners, will notice, and be inspired to fix the puzzle. As you will see, there's a simple change that could be made that would make everything work correctly.

The puzzle.

So here's the puzzle in question; as of this writing, you can still find the original here.
Four movie actors are in a cafe, sitting together at a square table, like the one shown here with the seats numbered. [The accompanying picture shows the seats numbered clockwise, 1 through 4.] They are discussing their most recent projects while waiting for their salads. Each has just returned from a different location where he or she was shooting a different type of film, one of which is a costume drama.

From the information provided can you figure out where each person sat, his or her full name, the location he or she had just returned from, and the type of movie each had shot?

  1. York (who isn't sitting in seat #1) shot a science fiction movie.
  2. The person sitting in seat #2 didn't just return from Tokyo.
  3. Julia is in seat #3.
  4. Hannah (who isn't sitting in seat #4) is across from the person who just returned from Hawaii.
  5. Marks is sitting next to the person who just returned from Spain.
  6. Moon did not shoot an action thriller.
  7. Glory and Robert are sitting next to each other; one of them is surnamed Smith and the other had just returned from Ireland.
  8. Robert (who isn't Moon) shot a romantic comedy.

There are no tricks, pure logic will get you the correct answer. And yes, there is enough information to arrive at the only correct answer.

Note in particular that the final sentence says there is a unique correct answer.

The problem with the puzzle.

There are five possible arrangements of given names, surnames, movie locations, and genres that satisfy the 8 conditions of the logic problem. They are:

Solution #1
Seat Name Surname Location Genre
1 Glory Moon Ireland costume drama
2 Hannah York Spain science fiction
3 Julia Marks Tokyo action thriller
4 Robert Smith Hawaii romantic comedy

Solution #2
Seat Name Surname Location Genre
1 Glory Marks Ireland action thriller
2 Hannah York Spain science fiction
3 Julia Moon Tokyo costume drama
4 Robert Smith Hawaii romantic comedy

Solution #3
Seat Name Surname Location Genre
1 Glory Marks Ireland action thriller
2 Hannah Moon Spain costume drama
3 Julia York Tokyo science fiction
4 Robert Smith Hawaii romantic comedy

Solution #4
Seat Name Surname Location Genre
1 Robert Marks Ireland romantic comedy
2 Hannah York Spain science fiction
3 Julia Moon Tokyo costume drama
4 Glory Smith Hawaii action thriller

Solution #5
Seat Name Surname Location Genre
1 Robert Marks Ireland romantic comedy
2 Hannah Moon Spain costume drama
3 Julia York Tokyo science fiction
4 Glory Smith Hawaii action thriller

You should take a moment to verify that all of these solutions meet the conditions of the logic puzzle.

No really, do it now; it will just take a minute.

So the logic puzzle does not have a unique solution.

The Coudal Partners Official Solution.

The solution presented on the Coudal Partners site does not address this problem. They present the first of the five solutions above as being “the” solution and they give an incorrect argument to support this claim. Here is their reasoning, up to the point where it is mistaken:
So at this point in the reasoning, we know the following:

Partial solution
Seat Name Surname Location Genre
1 Robert or Glory   Ireland  
2 Hannah   Spain  
3 Julia   Tokyo  
4 Glory or Robert Smith Hawaii  

The next step in the Coudal Partners answer is:

And this step is unjustified. Clue #5 says that “Marks is sitting next to the person who just returned from Spain”, and this only tells us that Marks is in either seat #1 or seat #3. In the first of the solutions given above, Marks is in seat #3. In the other four solutions, Marks is in seat #1.

What probably went wrong.

Probably, the fifth clue in the puzzle should have been
5. Marks is sitting to the left of the person who just returned from Spain.
In this case, Solution #1 (above) would be the only solution. So to fix the puzzle, all that needs to be done is to replace “next to” with “to the left of” in clue #5.

The obnoxious solution.

Of course, one could say that the puzzle as given does have a unique answer. That answer is “No”. That's because the question is
From the information provided can you figure out where each person sat, his or her full name, the location he or she had just returned from, and the type of movie each had shot?

What next?

I don't know. I hope that someone at Coudal Partners will take notice of this page or of some other page that points out the problem, and will fix the puzzle. It's perhaps a little awkward for them, since they had a competition to solve this puzzle and have declared winners and awarded prizes and all, but what else can they do but correct their mistake?

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