Pavel's Puzzle Blog

In the summer of 2009, at the annual International Puzzle Party, we were treated to a talk by the justly renowned computer scientist, mathematician, and author (and all-around Really Nice Guy™) Donald Knuth. He spoke about some of his favorite puzzles and some new puzzle ideas he'd been working on. As part of the presentation, he passed out a sheet of paper with several puzzles on it for us to solve later.

One of the entries on the paper was a description of an interesting set of twelve trominoes (aka triominoes), pieces made up of three unit squares joined in a little 'L' shape. Each piece had a line drawn on it (on both sides, so you could flip the pieces over), and your goal was to arrange them into a six-by-six square such that all of the lines formed a single, unbroken loop The solution, he said, was unique. OK, fun enough, but Don wasn't through, not by a long shot.

Then, he listed four more similar trominoes and said that, if you added those new pieces to the original ones, you could arrange them all into an eight-by-six rectangle, with the lines again forming a single continuous loop, and again the solution was unique. This was sounding even better, but he kept going!

Next, Don showed two more trominoes to add in, now enabling you to build a unique nine-by-six rectangle with the same properties. That was followed by yet two more trominoes, now forming a unique ten-by-six rectangle!

Finally, he showed four more tominoes you could add to everything that had gone before, with the entire set now making a nine-by-eight rectangle, still with the lines forming a single continuous loop, and still with a unique solution!

Five separate, progressively more difficult challenges, all from the same set of simple-seeming pieces, all with unique solutions: this was great, an elegant puzzle construction! There was only one teensy-tiny little problem: Don hadn't actually given us the puzzle! All we had was a description of the puzzle, stuck on this sheet of paper!

I immediately resolved to design a nice physical packaging of Don's puzzle idea, with all five challenges and all twenty-four tromino pieces included, along with a simple way to remember which pieces went with each challenge. The result is Tromino Trails. The initial six-by-six challenge isn't trivial, but also isn't particularly difficult. After that, each challenge poses a progressively tougher problem but also trains you, in a sense, to be ready for the challenge that follows.

My friend Stan Isaacs used this as his Exchange puzzle at this summer's International Puzzle Party in Berlin, and now I can make it available more broadly. I think it provides a very satisfying puzzle experience that's accessible to and enjoyable by both experts and new puzzlers alike.

Posted by Pavel at 02:43 PM | Permalink | Comments (0)

A couple of years ago, I was privileged to be commissioned to produce a unique, custom puzzle for the 2009 Science Foo Camp, a eclectic annual gathering of scientists sponsored by the journal Nature, by Google, and by O'Reilly Media. I ended up producing 300 copies of a special version of my then-new puzzle Anansi's Maze, which they then handed out to all of the attendees that summer. I was also invited to attend the event myself, which was truly wonderful, and they asked me back again the next summer. At the event in 2010, I started discussing with the organizers the possibility of my producing another puzzle for them for the 2011 gathering, this time a puzzle that had been designed from the beginning specifically with that event in mind.

I spent some time brainstorming puzzle themes with Kay Thaney from Nature, and we hit upon what I thought was a great inspiration. Tim O'Reilly, the founder of O'Reilly Media and one of the organizers of the event, has a favorite saying that he brings up at the introductory session of each Foo Camp:

When Tim says this, he's referring to the edges between intellectual disciplines, and how Foo Camp is designed to bring together people from different areas and enable a kind of creative friction as the areas butt up against one another.

When we brought up the saying in our puzzle-theme brainstorming, however, it immediately took on an entirely different meaning for me, and my mind began chewing over all sorts of ideas for embodying that meaning in a puzzle design. Edgewise is the result of that chewing. (Hm. That sounded better in my head than it reads here. Oh, well...)

Edgewise consists of about two dozen jigsaw-puzzle pieces, most with large letters etched on them, and some with additional words of potential significance. As this is the latest in my series of multi-stage puzzles, I won't say anything more about the solving experience here, but I can tell you that it should keep you happily busy for a little while as you make your way through it.

In the end, ironically, Edgewise did not wind up being used as a Science Foo Camp gift, but I remain grateful to Tim and Kay for providing the inspiration for this puzzle. We did use it in this summer's Microsoft Intern Puzzleday event, and I also used it for my Exchange puzzle at the International Puzzle Party in Berlin, so I think it's getting the kind of exposure it deserves, particularly because now it's available here on the website for you to try out for yourself!

Posted by Pavel at 02:43 PM | Permalink | Comments (0)

Even before I began designing my Anansi's Maze puzzle, I'd been thinking about how to create puzzles that intrinsically relied on the transparency of the pieces. My inspiration was a relatively unusual and little-known sub-genre of mechanical puzzles, sometimes called overlapping puzzles, in which the pieces have openings or transparent sections and your goal is to find a way to stack up those pieces and form a picture from the intersection of their transparent bits. The first puzzle I know of in this family was released way back in 1900, but there's been a steady trickle of examples ever since.

I got one such in the Puzzle Exchange at one of my first International Puzzle Parties. It consists of six octagonal pieces of transparent acetate, each laser-printed with a gray-scale image; if you stack up the pieces just right, the gray bits combine and darken and you end up with quite a nice picture of a dog, if I recall correctly. Mostly, I remember it being really difficult.

Still, the notion had stuck with me. I wanted to play in that design space, but I also wanted to make a puzzle that wasn't so tough to solve. I had the idea that I could make it easier by sharply reducing the number of layers, maybe using only two or three. To keep it from becoming trivial, I could break each layer into multiple pieces, so that you'd have to assemble the layers themselves before you could stack them up.

So far, so good, but then I got ambitious: what if you could assemble the layers in more than one way? What if you could form either of two different pictures from the same pieces, depending on which assembly you built? This whole story got me pretty excited: this could be a really cool puzzle! Now I just needed to actually design such a thing...

And there the idea sat, more-or-less unmoving, for almost two years.

The problem was, I had no idea how to go about creating this kind of a puzzle. Unlike many of my designs, I couldn't see any way to write software to help me search for a puzzle that would match my story; one of my key design tools had been stripped away from me!

I finally picked up the idea again late last winter, when I was trying to come up with a new mechanical puzzle for use in this summer's Microsoft Intern Puzzleday. There wasn't anything magical about the process, I just dug in, started drawing potential pictures, overlapping them, and looking for interesting area intersections. It was a very incremental, iterative design journey, one of the most difficult puzzle-design efforts I've been through. Even after I'd finished the artwork, what I'd thought of as the hard part of the process, the design went through five different prototype and test-solving iterations before I finally hit on the right combination of cleverness, accessibility, and clarity of solution.

In the end, ironically, the puzzle was completed too late to be used in Puzzleday, but I did use it as my Exchange at IPP 30 in Osaka later this past summer. I had barely enough copies made then to satisfy the Exchange rules, with just a few left over at the time for selling. By the time I finished with building those, I knew that I wanted to do yet one more, fairly minor design iteration before putting the puzzle up here on the website. What with one thing or another, it's taken me a while to do that iteration, but now it's done, and I'm quite happy with how the puzzle has turned out. I hope you'll enjoy it too!

Posted by Pavel at 10:42 PM | Permalink | Comments (0)

Take a 2x2 square, and join it to another 2x2 square, but only by half an edge. There's only one way to do that (ignoring reflections and rotations), shown below:

Back in 2002, my good friend Derrick Schneider noticed this nice little set of slightly strange shapes and wondered whether or not they'd make a good puzzle. He whipped up a little program to try packing the pieces into an 8x8 tray. To his delight (and later ours), there was just one way to fit in all four pieces! Many designers would have stopped there, but for some reason Derrick also tried running the program on a 7x9 rectangle: once again, incredibly, there was a unique solution!

Imagine the fun: he comes up with a simple way to define a set of pieces, the resulting set is nice and small, and that set fills both of the two most obvious tray shapes in unique ways. Believe me, such a mathematically elegant puzzle design doesn't come about every day! Add to that, the resulting puzzle falls into a real sweet spot of difficulty: harder than you might guess (those pieces are just plain tricky to get your brain around, especially the curled-up one), but easy enough to yield to a little patience.

Perhaps that explains why, when Derrick presented his puzzle at the 22nd annual International Puzzle Party, the jury for the Puzzle Design Competition awarded it an Honorable Mention, one of just three puzzles so honored.

Now, for the first time in many years, I'm happy to make Derrick's wonderful little puzzle available for sale again. Initially, I'll be selling off the remainder of Derrick's original manufacturing run; the last time I visited, I got him to dig around in the basement and pull out all of his old inventory for me. After that limited supply sells out (he could only find about 15 of them), I'll start making my own copies for you. This is simply too good a puzzle to remain unavailable for so long.

Update: Square Dance is now also available in this economical CD jewel-case edition! (Note: your tray and piece colors are likely to differ from what's shown in this photo. We use a wide variety of colors and every puzzle is made from a different pleasing assortment.)

Posted by Pavel at 04:25 PM | Permalink | Comments (0)

As I write this, I'm helping to host the first Microsoft Non-Intern Puzzleday, a re-run of the puzzles from this year's regular Intern Puzzleday, just to give the actual Microsoft employees a whack at them. I'm sitting outside a room in which I've set up six "solving stations" for the multi-stage mechanical puzzle I contributed this year, Anansi's Maze. (The Intern Puzzleday actually has a budget, so I could afford to give each team a copy of the puzzle; for the non-interns, they have to timeshare.)

This year, I wanted to play with transparency, as you could probably guess from the picture. I started out with a much more complex puzzle idea, but whittled it down, stage by stage, to get something that was a more appropriate level of difficulty and that hung together more completely. The result, I think, is my best multi-stage puzzle yet, so I decided to also use it for my 2009 Exchange puzzle at the International Puzzle Party in San Francisco.

Anansi the Spider is the trickster spirit of Caribbean and Western African myth and legend, known for his creative mischief making. This puzzle will tease you with its ambiguities and lead you on a merry chase to find its hidden meaning.

Here is a maze, Anansi tells us, but there are no walls, no paths to follow, let alone any dead ends or cycles. Our treasured ‘right-hand rule’ is useless in these uncharted territories.

Anansi’s Maze is a multi-stage solving experience: finding the solution to one stage leads to a new puzzle, and that one to another! Where does this pathless path lead? Can you see through all of Anansi’s tricks and find the answer he’s left for you at the end of your journey?

Posted by Pavel at 06:32 PM | Permalink | Comments (0)

Last year, my puzzle-design mind kept drifting to polyhedra, specifically to ways for pieces representing the faces of polyhedra to connect and interact with one another at each edge. My Octamaze and Gamesters of Triskelion puzzles came out of this realm, and for my IPP 2008 Exchange puzzle, I wanted to move up from the octahedron to my favorite of the Platonic solids, the dodecahedron. My experience with the tab-and-slot mechanism of the earlier puzzles, though, had made me very dubious that such an approach would continue to work for the rather larger dihedral angle of the dodecahedron: the tab would be coming into the slot at such a shallow angle that the slot would have to be quite wide, and the piece deformation needed to insert the last face probably wouldn't work at all, let alone elegantly.

I also wanted to use a prettier material than the opaque black high-impact polystyrene I'd used before, and that ruled out pretty much any piece deformation at all. (I'd tried making Octamaze out of acrylic, since it takes etching much better than polystyrene does, but after having my acrylic prototype shatter in my hands during disassembly, I gave up and went with the much more robust and pliant polystyrene.)

I decided that the pieces would rotate into position, using some kind of interlocking, hook-shaped protrusions on the edges of each face; that would still entail fairly wide (deep?) hooks, due to the shallow angle, but avoid any piece deformation during assembly. I realized that I might run into a mechanical problem with the corners of the faces hanging up on one another as each face was rotated into position, so I started considering various piece shapes that were missing the face corners. I started playing around with actual shapes on paper, instead of just thinking about all of it, and all of this came together in a kind of practical lesson in geometric duality: the hooks would be on the ends of arms, and the puzzle would look like stars with interacting points rather than the regular polygonal faces I'd originally imagined.

The resulting puzzle is probably the prettiest one I've ever designed, once assembled: it would make a great Christmas ornament, or an attractive object to dangle from the rear-view mirror of your car, let alone just sitting on your desk at work. It's also quite a difficult puzzle, so keep that in mind if you buy a copy. Like all of my puzzles, it comes with the solution, though, so nobody need know if you decide to short-circuit the solving and jump to the pretty bit.

[Update 8/27/2011: I've renamed this puzzle to "Crystal Ball", which I think describes it better than the old name, not to mention avoiding potential trademark issues... :-)]

Posted by Pavel at 05:21 PM | Permalink | Comments (3)

I originally blogged about this puzzle a couple of years ago, shortly after I got my first copy of it, six years in the making. A few days after that, I got email from my friend George Miller, telling me that he'd laser-cut his own copy and liked it a lot. He showed that copy to long-time IPP attendee Stan Isaacs, who asked me for permission to use it in the IPP 26 Exchange, in Boston. At the time, I had a different puzzle in mind for my own exchange gift, so I agreed. Unfortunately, that other idea fell through (sometimes that happens with puzzle designs), so I ended up not exchanging that year. Instead, I was Stan's exchange assistant, which was fun in its own way.

The version that Stan exchanged was somewhat different from my original copy: he and George reshaped the pieces from rectangles to half circles, making the completed puzzle into a sphere instead of a cube; they called it the "Fan-Way Park Ball", following the Bostonian theme. They also used laser-cut maple instead of plastic and reduced the size to about 1-5/8 inches. It was cute in its own way, and I was happy to see the puzzle exchanged, but I still preferred the clear Lucite look of my original version; it looks a bit more stylish sitting on your desk.

I'm now happy to announce that I can offer copies of my version for sale here. The puzzle is shipped disassembled, flat, and putting it together provides a very satisfying but accessible solving experience.

[Update 8/27/2011: I've renamed this puzzle from "Six Tabbed Planks" to the more euphonious "Finnish Cross", in honor of its original designer, Matti Linkola. It's still the same great puzzle, just with a spiffy new name!]

[Update 4/9/2012: I now have The Finnish Cross available in three jewel-tone colors, in addition to the original crystal clear. Check it out!]

Posted by Pavel at 02:56 PM | Permalink | Comments (3)

Flush with the successful design of the "Perkinson Guest Bathroom Tile" puzzle, the obvious next step was to consider dominoes instead of trominoes. This time, I allowed the pieces to be flipped over, and I also counted pieces whose two tiles had their tilted edges at right angles to each other. This leads to a complete set with 13 members, some of which are slightly strange looking, and one of which (with the two tilted edges joined together) is a quite boring perfect rectangle.

Leaving out the boring rectangle, we get twelve roughly one-by-two-unit dominoes; the obvious tray shape is a six-by-four-unit rectangle. Can the (nearly) complete set fill that tray? Sadly, my packing program said no, and this time it also didn't work to change the top and bottom edges into the angular "sine wave" pattern from the bathroom-tile puzzle. I had my local laser cutter, Joe Pelonio, make me up a set of the pieces anyway, so that I could play with them and try to get a feeling about why the rectangular tiling wouldn't work. The first thing I noticed when I got the pieces in my hands was that one of them looked a lot like the profile of one of the famous "moai" heads from Easter Island; thus the eventual name of the puzzle.

When I presented Easter Island Dominoes at the 2007 IPP Exchange in Australia, I told the following story:

It's not well known (especially to archaeologists), but many, many sets of these 12 pieces have been discovered in excavations on Easter Island. Never, though, have they come across a copy of that elusive 13th piece, the perfect rectangle. From this, we can infer that the ancient Easter Island culture, now long lost to us, did not approve of straight lines and perfect rectangles. Being a culturally sensitive fellow, I've created a tray that has one tilted tile edge exposed on each edge of the tray, thereby avoiding violating the islanders' taboos.

Your first challenge in solving this puzzle is simply to lay all twelve pieces flat in the tray; there are 250 ways to do that, and it's not very difficult if you just have a bit of patience. You'll find, though, that almost every such packing has at least one blemish (as least from the point of view of ancient Easter Island culture): there will either be (a) a straight-line crack all the way across or down the puzzle, or (b) a subset of the pieces that form a perfect rectangle or square, or (c) both!

There are just 83 ways to pack the pieces without a straight-line crack, and only six ways to do so without forming a perfect square or rectangle. Your real challenge is to find one of merely three solutions that have neither "blemish". That'll take you a little bit longer to achieve, I think.

Posted by Pavel at 07:53 PM | Permalink | Comments (0)

In the fall of 2004, I was playing around with a deceptively simple little tray puzzle designed by Stewart Coffin and called Four Sleazy Pieces. The eponymous pieces are polyominoes with between five and seven squares each, and the tray is a perfect square whose size is not an integral number of units; it's about 5.8 units on a side. I won't spoil Coffin's fine puzzle here, but suffice to say that, at the time, I hadn't solved it very recently so I'd temporarily forgotten just how "sleazy" the solution is.

While failing to solve it, I stumbled across an interesting property of such a puzzle, and I was excited to note that what I'd found was probably a good psychological "blind spot". These blind spots usually take the form of an assumption most people make that's so "obvious" that it's never questioned, even though it isn't in fact true. Armed with such a blind spot, you can often create a puzzle to exploit it, a puzzle whose solution violates that implicit assumption. That kind of a puzzle has a very pleasant "ah-ha" feeling to it; once you've solved it, you can't figure out how it could possibly have taken you so long.

My resulting puzzle, Sleazier, has that property, and I'm inordinately pleased with it: I think that it's probably the best puzzle I've yet designed. I presented it in the 2005 IPP Exchange, in Helsinki, and it's gotten great feedback in the years since then.

Like Coffin's puzzle, Sleazier has four polyomino pieces ranging from five to seven squares each, and a square tray of a suspiciously odd size; your goal is simply to fit all four pieces flat in the tray. I won't say why, here, but when you compare the "trick" of my puzzle to that of Coffin's, mine definitely deserves its name.

Update: Sleazier is now also available in this economical CD jewel-case edition! (Note: your tray and piece colors are likely to differ from what's shown in this photo. We use a wide variety of colors and every puzzle is made from a different pleasing assortment.)

Posted by Pavel at 07:49 PM | Permalink | Comments (3)

In my very first IPP Exchange, in 2000, I presented a puzzle designed by Bill Darrah, called Raft 5. It consisted of 10 sticks, each with a dovetail notch cut across it and a matching dovetail tab glued on along it. There were five different positions on the stick where a notch or tab could be located, for a total of 10 different pieces, and the puzzle contained one of each. Somewhat surprisingly, it's actually possible to assemble these 10 pieces in a raft-like arrangement, with five sticks going one way laid across five going at a right angle.

Raft 5 is a good puzzle, and for the 2003 Exchange in Chicago, I decided to take inspiration from it. The raft is essentially two dimensional, and I wanted to somehow extend the idea into 3-D. To keep the number of possible pieces down, I made my sticks shorter, with only three positions where a notch or tab could be placed, but I also made the sticks square in cross-section (as opposed to rectangular, as in the raft). This allowed tabs and notches to appear on different sides of the stick, even at right angles to one another.

If you leave out the cases where a notch and tab appear in the same position along the stick (unless they're on opposite sides of the stick), then you get a total of 14 possible pieces. That seemed like too many for a good puzzle, so I picked just half of them; I was perversely tickled by the idea of using seven pieces in an interlocking puzzle, instead of the traditional six. Of course, seven pieces can't make a very symmetric shape, but I made a virtue of that, and designed the puzzle so that the final shape isn't particularly important. Instead, the goal is simply to arrange the pieces so that every piece's tab is inserted into some other piece's notch; that forms the pieces into a kind of folded-up loop, each inserted into the next, like a snake eating its own tail.

There are four solutions to the puzzle, two of which have the fun property that the resulting assembly will balance nicely on the end of one of the sticks. Those two solutions look a bit like a figure standing on one foot, which I like quite a lot; at some point, I want to make a very large set of the pieces to use as a bit of artwork for our yard.

Update (2019):

After being sold out for many years, the Devil's Half Doven is finally available again! I am delighted to bring this design back to life, now in 3-D printed form! The original design is lovingly preserved, and now it's joined by a completely new, smaller relative, the Devil's Mini Doven! This new design uses five of the 14 possible pieces that weren't included in the original version, and has just two solutions. It's definitely a bit easier than its original cousin, but still puts up a nice little fight. In particular, interestingly, most people who succeed in finding one solution seem to have a really hard time finding the other one! Will you be the exception? (If you combine these two puzzles, it might be possible to assemble all 12 pieces. Please let me know if you manage this feat, and send a photo!)

Posted by Pavel at 07:40 PM | Permalink | Comments (2)

For the 2002 puzzle party in Antwerp, I wanted to design something that would lead people to explore the strange world of Penrose's non-periodic kite-and-dart tiles. Some years earlier, someone else had already exchanged a Penrose-based puzzle; that one was just a set of kites and darts that had been distorted a bit to resemble two kinds of birds (and to enforce the normal edge-matching rules). The goal had been simply to fit them together to make the classic regular decagon that crops up every you look in any tiling.

For my own puzzle, I wanted to challenge you to do more than simply learn how to tile the pieces; I wanted it to be a real puzzle. I played around with a Penrose tiling applet for a while and came up with an outline that looked, to me anyway, a lot like the head of a man wearing a turban. That shape required 76 tiles to make, so I broke it up into a set of 16 multi-tile pieces, each containing between 3 and 5 tiles. I then laser cut and etched those pieces with Conway's beautiful curves that show where the legal edge matches are. The resulting puzzle has a unique solution and is fairly difficult.

To make it a bit easier, I added a little removable panel that reveals where some of the tile boundaries are (and that shows why I thought the shape looked like a Grand Vizier). I also included in the package a "little bit bigger hint" that shows where all of the tile boundaries are (but not the piece boundaries, of course).

Finally, I discovered that a subset of pieces I'd chosen could be assembled to form that same classic decagon I mentioned above, so I made the puzzle tray two sided, with the outline of the Grand Vizier on the front and the outline of the decagon on the back. Oddly enough, even though I don't tell you which subset of the pieces you have to use in filling the decagon tray, that side is definitely easier than the front.

Posted by Pavel at 12:40 AM | Permalink | Comments (0)

In 2001, the 21st annual International Puzzle Party was held in Tokyo, and I decided to honor the hosts with a puzzle based on the simple, elegant design of the Japanese flag, also known as Hinomaru (literally, "the circle of the sun"). To start, I drew the flag's design on a 6-by-4 rectangle and then broke it up into twelve 1-by-2 dominoes. Then, to make things tricky, I also colored the backs of all of the dominoes in ways that make them look like potential fronts. Thus, all of the dominoes are double-sided, and it's not at all obvious which side is the front! Add to this the high degree of symmetry in the flag design, which makes the piece placements even more ambiguous, and you have a very difficult puzzle.

(At the 2007 IPP in Australia, six years later, someone came up to me during the Exchange and said, "I spent a long, long time solving that flag puzzle of yours." He then handed me his Exchange puzzle. "This," he said, "is my revenge!" Needless to say, I haven't solved his puzzle yet...)

The Hinomaru puzzle has a unique solution (up to swapping pieces with the same face-up design), and that solution leaves only the front face looking like the flag; the backs of the pieces look entirely random when solved (no helpful hints there!).

I also have an all-paper version of the puzzle, consisting just of the 12 double-sided cards that are sandwiched inside clear acrylic in the version above. This version doesn't come with a tray, just the cards wrapped up in a simple origami envelope.

Posted by Pavel at 11:20 PM | Permalink | Comments (0)

When I was invited to my first International Puzzle Party in 1999, in London, I learned that I would not be allowed to participate in that year's Puzzle Exchange event. There's a very good rule that you need to have attended IPP once before you do the Exchange, to give you a chance to soak up a bit of the party's culture and quality expectations. I decided, though, that I would produce some kind of puzzle anyway, so that I could try to trade it informally for Exchange puzzles (and others).

The only problem was that I had never designed a puzzle before! I mentioned this issue to my friend Barry Hayes and his response was both surprising and surprisingly helpful: "There are puzzles all around us! Almost everything you see is a puzzle; the only tricky part is to recognize how."

As it happened, I was in the local home center the next weekend, buying parts for our garden sprinkler system. Surrounded by all these very uniform pipes and fittings, Barry's words came back to me and I decided that there must be lots of puzzles hidden in these bins. The first thing that came to mind, of course, was a puzzle involving water moving through the pipes, but it didn't take me long to reject that idea in favor of something, anything, less complicated, less "analog". But what else would neatly fill a pipe? Well, anything round would, like ball bearings and dowels...

The result, Pavel's Pipe Dream, is shown at right. There are five dowels, one starting inside each pipe, with notches on the dowels intersecting (and therefore interacting) inside each T fitting. The ball bearing starts just inside the (sealed) endcap in the lower left corner. To solve the puzzle, you must manipulate the dowels through the little windows in the pipes to eventually free the ball. I brought more than 50 copies of the puzzle to London, and succeeded in trading all of them (and the promise of another dozen or so more) to various of the attendees. I came back home after the party drunk with the fact that I'd added something like 65 new puzzles to my collection!

I don't have any more assembled copies of this puzzle left, but I've got lots of copies of the various bits and pieces lying around in the shop. It's not my favorite of my designs, but perhaps if there's sufficient demand I'll produce one more run of them for sale. Leave a comment if you might be interested.

Posted by Pavel at 01:24 AM | Permalink | Comments (0)

Last Saturday, we held one of the three central events of the annual International Puzzle Party here in Helsinki, the Edward Hordern Puzzle Exchange. This is, in many ways, the most highly anticipated event of the party, with most participants beginning to prepare for it starting back in December, if not earlier. This year, we had 91 people taking part in the Exchange, out of about 170 puzzlers attending the party overall.

The Exchange was scheduled to begin at 10am, and we got access to the hall, to prepare, starting at 9:30. Tables had been laid out in long lines across the room, one table and two chairs per exchanger (one chair for each puzzle's presenter, and one for their assistant, if any). Every table had an exchanger's nametag on it, and there was a schematic map at the entrance, to make it easier to find your station. On the stage at the front of the hall, there was another, shorter, line of empty tables, intended to hold samples of all of the exchange puzzles.

At my table, my assistant Michael Powell and I got to work unpacking the big box I'd brought in containing the puzzles I'd had made back home and then shipped ahead of me to Helsinki. We needed to work somewhat quickly, because I'd discovered the previous day that, during shipping, the sharp laser-cut edges of the puzzle trays had rubbed against one another, slicing many of their zip-loc bags into ribbons. We had to check every single bag and, in half or more of the cases, remove the puzzle and repack it into a new bag, purchased the previous day, with some effort, at a Finnish supermarket. (Do you know the Finnish word for "zip-loc"? Me neither.)

By 9:55 or so, we were ready, with one copy of my puzzle tagged and arranged on the samples table, and the other 91 (including one as a thank-you gift for Michael) stacked neatly in front of us on my table. Michael had our exchange checklist ready; all that remained was to wait for the signal to begin.

The Exchange is a heavily tradition-laden event that grew out of an ad-hoc practice at the earliest puzzle parties. Several of those early invitees brought little puzzle gifts for everyone else and handed them out. As the party grew, over the years, the Exchange was formalized and the key rules were set down. First, not every attendee at the party need take part in the Exchange; it's strictly voluntary, and only allowed for people who've been to at least one party previously. Second, every participant must bring many copies of the same puzzle, one for each other participant and one for the samples table; many people bring more, to offer for sale or trade at the official "Puzzle Party" the next day. Third, all Exchange puzzles must be original, never available before the day of the Exchange. Fourth, and most ambiguously, these must be high quality mechanical puzzles; paper-and-pencil puzzles, like crosswords, and jigsaw puzzles are not included. (The term "high quality" is intended to refer to the puzzle-solving experience, not necessarily to the materials or craftsmanship; in particular, "high quality" does not necessarily imply "high cost".)

At about 10:02am, this year's IPP host Tomas Lindén stepped up to the microphone and gave the signal: the 2005 Exchange was under way.

Over the course of the next five hours, Michael and I walked around the hall, meeting each of the other 90 exchangers, chatting a little bit, describing our puzzles to each other, and finally exchanging them. From time to time, Michael would carry the puzzles we'd received back to my own table and pick up another armload of my puzzles to give away. Since my table this year was off in a back corner of the room, we had a lot more success finding new exchangers by walking around the room ourselves. We tried a few times going back to my table and waiting for others to come to us, but with only marginal results.

By the end of the five hours, we'd checked off everyone on our list and Michael had packed up all of my swag in the boxes I'd brought. Another Exchange had come to an end.

I haven't had a chance yet to really take stock of the puzzles I received this year. There's always a few disappointing ones, and usually some pretty special ones, and I don't expect this year to be any different. I've already solved a few of them (an amusingly misleading tray-packing puzzle, a simple "Finnish thematic" tray puzzle, a level 7-3 three-piece burr, and a 39-move sliding block puzzle), and I've brought a few more with us on our trip to Norway, but the big review will have to wait until we and the boxes I shipped both arrive back home in the States.

What a cool thing to look forward to!

Posted by Pavel at 07:01 AM | Permalink | Comments (0)

I'm writing this from my hotel room in Helsinki, at about 5:00am local time. Kathleen and I arrived yesterday afternoon and, of course, the ten-hour jet lag is causing a little sleep-cycle disruption.

We're here for the 25th annual International Puzzle Party (IPP), an invitational gathering of serious collectors of mechanical puzzles. The definition of "serious" is pretty vague, but is intended to exclude the merely curious. (Though, as anyone here would admit, there are a number of pretty curious people here nonetheless.) To give you a sense of how serious "serious" can be, though, my collection of 600-700 puzzles is well down at the low end of the size distribution. There are many people here with several thousand puzzles, and a few amazing collections of 25,000 or 30,000 puzzles or more, some dating as far back as the 13th century. Believe me, Kathleen's getting off easy in the "whacko spouse" department (as least as regards collections).

The party location rotates every three years among Europe, the United States, and Asia. There will probably be around 200 collectors here, many with their families, from 25-30 countries all over the world.

The party doesn't actually start for a few more days yet, but we decided to come early to give ourselves extra time to explore the area and to get over our jet lag. To our inexplicable surprise, several other folks had the same idea, so the puzzle conversations have already started echoing around the lobby here.

I hope to be posting pretty actively for the next while, so keep checking back for more on Helsinki, puzzles, and Norwegian coastal cruises!

Posted by Pavel at 06:48 PM | Permalink | Comments (0)