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      <title>Pavel&apos;s Puzzle Blog</title>
      <link>http://www.pavelspuzzles.com/</link>
      <description>All kinds of puzzles: some for sale, some for free, many just written about</description>
      <language>en</language>
      <copyright>Copyright 2012</copyright>
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         <title>Holiday Discount Puzzle 2011</title>
         <description><![CDATA[<h2>A Holiday Discount Puzzle</h2>
<h3>Solve this puzzle for 10% off any order!</h3>

<p>I had so much fun with last year's holiday-discount-puzzle promotion that I've decided to do it again!  Who knows, maybe it'll turn into an annual tradition around here...</p>

<p>Just like last year, in honor of the holiday season, I've created a puzzle that you can solve to earn a discount on any order here at Pavel's Puzzles.  Simply cut out the fourteen strips linked to by the image below, cutting along the heavy lines.  Then weave them together into a square with seven strips placed horizontally and seven placed vertically, such that you can see all of the letters.  (Ignore the orientations of the letters.  I've scrambled them to avoid giving you too much information.  Heh.)  Finally, read out the message to learn the secret discount code!</p>

<div class="product-image-right">
<script>PopUpPDF("holiday-2011");</script>
</div>

<p>Once you know the answer, make any order at Pavel's Puzzles and type the answer into the "Instructions to Seller" space on the PayPal checkout form.  When I get the order, I'll issue you a refund for 10% of the cost of your order!  (Sales tax and/or shipping excluded.)  Even better, you can get the same discount on as many orders as you like between now and the end of this year!</p>

<p>To further spur you into action, I've just released three new puzzle designs:</p>

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<script>PopUpTiny("edgewise2");</script>
</div>

<p><a href="http://www.pavelspuzzles.com/2011/11/edgewise.html">Edgewise</a> is just a simple little jigsaw puzzle, isn't it?  With only a couple dozen pieces or so, how difficult could it be?  This was my Exchange puzzle at the International Puzzle Party in Berlin this summer, and it's the latest in my series of multi-stage solving experiences, sure to keep your mind occupied for a little while.</p>

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<script>PopUpTiny("trominoes2");</script>
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<p>World-renowned computer scientist Donald Knuth conceived of this puzzle a few years ago and I've designed this elegant physical realization of his five progressively more difficult challenges: can you fit the pieces into the tray such that the <a href="http://www.pavelspuzzles.com/2011/11/tromino_trails.html">Tromino Trails</a> form a single continuous loop?  Each challenge has a unique solution and helps &lsquo;train&rsquo; you to be ready to take on the next one.</p>

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<script>PopUpTiny("icicle");</script>
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<p>This big, icy beauty is perfect for those coming winter nights in front of a fire.  <a href="http://www.pavelspuzzles.com/2011/11/icicle_jam.html">Icicle Jam</a> was inspired by the startlingly blue ice of Alaskan glaciers and once you've assembled it you'll have a display piece that will be a striking addition to any room.  Of course, first you'll have to survive its jagged interlocking challenge.  Dress in layers, and make sure someone knows where you've gone!</p>

<p>Of course, I still offer all of my earlier designs, too.  My holiday discount puzzle is a perfect way to satisfy (or frustrate) that puzzling person on your gift list while saving a little cash at the same time.  Just imagine the look on their face when they find one of these puzzles in their stocking!</p>]]></description>
         <link>http://www.pavelspuzzles.com/2011/11/holiday_discount_puzzle_2011.html</link>
         <guid>http://www.pavelspuzzles.com/2011/11/holiday_discount_puzzle_2011.html</guid>
         <category>Multi-stage puzzles</category>
         <pubDate>Sat, 26 Nov 2011 18:18:54 -0800</pubDate>
      </item>
            <item>
         <title>Icicle Jam</title>
         <description><![CDATA[<p>One of my best-selling puzzles is the <a href="http://www.pavelspuzzles.com/2007/09/six_tabbed_planks_1.html">Finnish Cross</a> (formerly known as Six Tabbed Planks), designed by <a href="http://www.tutka.net/~linkola/">Matti Linkola</a>.  That might be simply because it's one of the least expensive puzzles on the website, but I prefer to think that it's because it has a compact elegance about it that makes it fit well on a executive's desk or anywhere else.  I have received one or two letters about it, though, from purchasers who were disappointed at its overall size (about two inches cubed).</p>

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<script>PopUpProduct("icicle3");</script>
</div>

<p>In its pure form, though, the puzzle has a certain fixed aspect ratio: if I made one twice as large, it would necessarily be made from plastic that was twice as thick (1/2 inch instead of 1/4 inch).  It's a slow and tedious process to laser cut such thick acrylic, and some artifacts of the cutting process get magnified as well.</p>

<p>For example, the laser doesn't cut a channel that's at a perfect right angle to the surface; the channel is more V-shaped, wider on the 'entry' side and narrower on the 'exit' side, so the pieces end up being slightly trapezoidal in cross section rather than rectangular.  Now, proper laser-cutting technique can significantly mitigate such tendencies, but as you scale up to thicker and thicker materials, the artifacts start to overwhelm the mitigations.  For a 3D interlocking puzzle like the Finnish Cross, the result wouldn't be as satisfying as I'd like.</p>

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<script>PopUpProduct("icicle2");</script>
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<p>One morning, as I pondered this 'size matters' issue, I idly noted that I had managed to build up a small inventory of fluorescent blue acrylic, originally intended for use on a commission where we ended up going in a different direction.  That plastic had always put me in mind of the shockingly blue ice we'd seen on <a href="http://www.smithsonianjourneys.org/blog/wp-content/uploads/2009/04/alk_glacier_calving_ss_blog1.jpg">Alaskan glaciers</a>, and now that led me to picture a version of the Finnish Cross that looked like a whole bunch of icicles had been jammed together into a kind of starry, snowflakey shape.  The idea really appealed to me, and I immediately sat down with my drawing software.  A few hours of design later, I was ready to try cutting out the first prototype for Icicle Jam, and the result was just as striking as I'd imagined.</p>

<p>This jagged, icy beauty is big, about 6-1/2 inches in diameter, and really eye-catching in any setting.  The internal interlocking configuration is the same as in the Finnish Cross, but I find it's a little bit tougher to visualize it in this new, more flamboyant form, making for a slightly more difficult solving experience.  If you're looking for a satisfying puzzle that will really remind you of its sub-Arctic roots, Icicle Jam may be just the ticket!</p>

<p><script>AddToCart("icicle");</script></p>]]></description>
         <link>http://www.pavelspuzzles.com/2011/11/icicle_jam.html</link>
         <guid>http://www.pavelspuzzles.com/2011/11/icicle_jam.html</guid>
         <category>Mechanical puzzles</category>
         <pubDate>Sat, 26 Nov 2011 15:37:25 -0800</pubDate>
      </item>
            <item>
         <title>Tromino Trails</title>
         <description><![CDATA[<p>In the summer of 2009, at the annual <a href="http://www.pavelspuzzles.com/international_puzzle_party_ipp/">International Puzzle Party</a>, we were treated to a talk by the justly renowned computer scientist, mathematician, and author (and all-around Really Nice Guy&trade;) <a href="http://en.wikipedia.org/wiki/Donald_Knuth">Donald Knuth</a>.  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.</p>

<p>One of the entries on the paper was a description of an interesting set of twelve <i><a href="http://en.wikipedia.org/wiki/Tromino">trominoes</a></i> (aka <i>triominoes</i>), 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.</p>

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<script>PopUpProduct("trominoes2");</script>
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<p>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 <i>eight</i>-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!</p>

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

<p>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!</p>

<p>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 <i>description</i> of the puzzle, stuck on this sheet of paper!</p>

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<script>PopUpProduct("trominoes3");</script>
</div>

<p>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.</p>

<p>My friend Stan Isaacs used this as his <a href="http://www.pavelspuzzles.com/2005/07/ipp_25_puzzle_exchange.html">Exchange</a> 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.</p>

<p><script>AddToCart("trominoes");</script></p>]]></description>
         <link>http://www.pavelspuzzles.com/2011/11/tromino_trails.html</link>
         <guid>http://www.pavelspuzzles.com/2011/11/tromino_trails.html</guid>
         <category>International Puzzle Party (IPP)</category>
         <pubDate>Sat, 26 Nov 2011 14:43:43 -0800</pubDate>
      </item>
            <item>
         <title>Edgewise</title>
         <description><![CDATA[<p>A couple of years ago, I was privileged to be commissioned to produce a unique, custom puzzle for the 2009 <a href="http://www.nature.com/natureconferences/scifoo/index.html">Science Foo Camp</a>, 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 <a href="http://www.pavelspuzzles.com/2009/08/anansis_maze.html">Anansi's Maze</a>, which they then handed out to all of the attendees that summer.  I was also invited to <a href="http://www.youtube.com/watch?v=51YmoYxxwaQ">attend the event myself</a>, 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.</p>

<p>I spent some time brainstorming puzzle themes with <a href="http://kaythaney.wordpress.com/">Kay Thaney</a> from Nature, and we hit upon what I thought was a great inspiration.  <a href="http://twitter.com/timoreilly">Tim O'Reilly</a>, 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 <a href="http://www.keltis.us/blog/archives/2005/08/what_i_did_at_f_1.html">Foo Camp</a>:</p>

<div style="margin: 0px 20px; font-style: italic">
&ldquo;All of the most interesting stuff happens at the edges.&rdquo;
</div>

<p>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.</p>

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<script>PopUpProduct("edgewise2");</script>
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<p>When we brought up the saying in our puzzle-theme brainstorming, however, it immediately took on an entirely <i>different</i> 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...)</p>

<p>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 <a href="http://www.pavelspuzzles.com/multistage_puzzles/">multi-stage puzzles</a>, 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.</p>

<p>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 <a href="http://www.pavelspuzzles.com/microsoft_intern_puzzleday/">Microsoft Intern Puzzleday</a> event, and I also used it for my <a href="http://www.pavelspuzzles.com/2005/07/ipp_25_puzzle_exchange.html">Exchange</a> puzzle at the <a href="http://www.pavelspuzzles.com/international_puzzle_party_ipp/">International Puzzle Party</a> 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!</p>

<p><script>AddToCart("edgewise");</script></p>]]></description>
         <link>http://www.pavelspuzzles.com/2011/11/edgewise.html</link>
         <guid>http://www.pavelspuzzles.com/2011/11/edgewise.html</guid>
         <category>International Puzzle Party (IPP)</category>
         <pubDate>Fri, 25 Nov 2011 14:43:47 -0800</pubDate>
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            <item>
         <title>Holiday Discount Puzzle 2010</title>
         <description><![CDATA[<h2>A Holiday Discount Puzzle</h2>
<h3>Solve this puzzle for 10% off any order!</h3>

<p>In honor of the holiday season, I've created a puzzle that you can solve to earn a discount on any order here at Pavel's Puzzles.  Simply cut out the pieces below and assemble them into the shape shown; then find the clues to the one-word final answer.  (Ignore any words shorter than four letters.)  The final answer is just three letters long (or five, depending on which form you prefer).</p>

<div class="product-image-right">
<script>PopUpPDF("holiday-2010");</script>
</div>

<p>Once you know the answer, make any order here and type the answer into the "Instructions to Seller" space on the PayPal checkout form.  When I get the order, I'll issue you a refund for 10% of the cost of your order!  (Sales tax and/or shipping excluded.)  Even better, you can get the same discount on as many orders as you like between now and the end of this year!</p>

<p>To further entice you, I've just released two new puzzle designs:</p>

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<script>PopUpTiny("get-a-clue");</script>
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<p>This puzzle is shaped like a magnifying glass, but the glass has been broken!  Reassemble the glass in two different ways to reveal clues to a mystery!  "<a href="http://www.pavelspuzzles.com/2010/11/get_a_clue.html">Get a Clue!</a>" was my Exchange puzzle at this summer's International Puzzle Party in Japan, and I've finally finished the minor revisions I wanted to make before releasing it on the website.</p>

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<script>PopUpTiny("eights-easy");</script>
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<p><a href="http://www.pavelspuzzles.com/2010/11/easy_eight_hard_eight.html">Easy Eight / Hard Eight</a> is a lovely little tray puzzle designed by my friend Bob Hearn: just pack the letters of the word "EIGHT" into each side of the tray.  The "easy" side isn't <em>too</em> tricky, but the "hard" side will keep you busy for a while...</p>

<p>These two join two more new designs I released late this summer:</p>

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<p>In Derrick Schneider's <a href="http://www.pavelspuzzles.com/2010/08/square_dance.html">Square Dance</a> puzzle, there are just four simple-seeming pieces to fit into each side of the tray, but they're much trickier to get your head around than you'd think, and there's only one solution per side!  This award-winning puzzle design is available again for the first time in many years!</p>

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<script>PopUpTiny("calibron");</script>
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<p><a href="http://www.pavelspuzzles.com/2010/08/the_calibron_12block_puzzle.html">The Calibron 12-Block Puzzle</a> was originally copyrighted in 1932 by the son of Thomas Edison; it has been unavailable for over half a century. Can you assemble the 12 blocks into a single, solid rectangle?  Just how easy a puzzle do you think an Edison would design?</p>

<p>Of course, I still offer all of my earlier designs, too; it's a perfect way to satisfy (or frustrate) that puzzling person on your gift list.  Just imagine the look on their face when they find one of these puzzles in their stocking!</p>]]></description>
         <link>http://www.pavelspuzzles.com/2010/11/holiday_discount_puzzle_2010_1.html</link>
         <guid>http://www.pavelspuzzles.com/2010/11/holiday_discount_puzzle_2010_1.html</guid>
         <category>Multi-stage puzzles</category>
         <pubDate>Tue, 23 Nov 2010 23:06:14 -0800</pubDate>
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            <item>
         <title>Get a Clue!</title>
         <description><![CDATA[<p>Even before I began designing my <a href="http://www.pavelspuzzles.com/2009/08/anansis_maze.html">Anansi's Maze</a> 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 <i>overlapping puzzles</i>, 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.</p>

<p>I got one such in the <a href="http://www.keltis.us/puzzles/2005/07/ipp_25_puzzle_exchange.html">Puzzle Exchange</a> at one of my first <a href="http://www.keltis.us/puzzles/2005/07/hello_from_helsinki.html">International Puzzle Parties</a>.  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 <i>really</i> difficult.</p>

<p>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.</p>

<p>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...</p>

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

<p>The problem was, I had no idea <i>how</i> 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!</p>

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<script>PopUpProduct("get-a-clue");</script>
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<p>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 <a href="http://www.pavelspuzzles.com/microsoft_intern_puzzleday/">Microsoft Intern Puzzleday</a>.  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.</p>

<p>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!</p>

<p><script>AddToCart("get-a-clue");</script></p>]]></description>
         <link>http://www.pavelspuzzles.com/2010/11/get_a_clue.html</link>
         <guid>http://www.pavelspuzzles.com/2010/11/get_a_clue.html</guid>
         <category>Mechanical puzzles</category>
         <pubDate>Tue, 23 Nov 2010 22:42:21 -0800</pubDate>
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            <item>
         <title>Easy Eight / Hard Eight</title>
         <description><![CDATA[<p>As I've described <a href="http://www.pavelspuzzles.com/2008/05/octamaze.html">before</a>, there's a marvelous biennial conference in honor of <a href="http://en.wikipedia.org/wiki/Martin_Gardner">Martin Gardner</a> called, appropriately enough, the Gathering for Gardner.  It brings together three communities that Martin was active in, and in which Martin was very influential: mathematicians, puzzle people, and stage magicians.</p>

<p>No, really.</p>

<p>Each conference has a theme, and that theme is the sequence number of that conference.  My first Gathering was the eighth one, so its theme was the number 8.  (Did I mention the mathematician connection?)  Anyway, everyone who comes to the conference is supposed to bring something for everybody else, all 300 or so of us, and ideally it will be something related to the theme number.  I thought I was pretty clever when I came up with a very <a href="http://www.pavelspuzzles.com/2008/05/octamaze.html">eight-related puzzle</a> to give everyone.</p>

<div class="product-image-right">
<script>PopUpProduct("eights-easy");</script>
</div>

<p>My friend <a href="http://www.dartmouth.edu/~rah/">Bob Hearn</a>, though, took literal-mindedness to a whole new level: he designed and gave out a puzzle that was entirely built out of the <i>word</i> "EIGHT".  He found a clever style in which to draw the letters in "EIGHT" so that there are lots and lots of ways to neatly link those letters together, and then he picked a particularly cute couple of those ways and turned each one into a tray-packing puzzle.</p>

<p>The "Easy Eight" side of the tray appears perfectly straightforward, just a simple square.  The problem is that it's kind of tricky to figure out how to get all five letters to lie flat in there at the same time: so many cute ways to fit the letters together, only one way to actually pack them into the tray.</p>

<div class="product-image-left">
<script>PopUpProduct("eights-hard");</script>
</div>

<p>Bob couldn't just leave it at that, though.  No, it wasn't enough for him to create a really clever and elegant puzzle.  He had to do it <i>twice</i>, with the same set of pieces.  The (unique) solution to the "Hard Eight" side of the tray is equally clever, and equally elegant, and <i>awfully</i> tricky to find!  It probably never occurred to you before, but an ellipse doesn't have any corners.  None at all.  There's no obvious way to start on this side, no clear surety that you're making any progress at all until, suddenly, there it is: the pieces are really, really close to fitting in.  A little more tweaking, some tiny adjustments, and then you realize you're <i>still</i> not putting them in correctly!</p>

<p>Ahem.  Sorry, got a little carried away there.  Just a little puzzle-frustration flashback.  I'm fine now.</p>

<p>As soon as I finally solved both of Bob's lovely Eights, I started talking with him about offering a version of his puzzle on this website.  It's taken me a long time to pull it together (the tolerances for the "Hard Eight" side are pretty tight), but I've finally succeeded, and now I can make this wonderful creation available to you.  This is a puzzle you'll enjoy solving yourself, and then really enjoy torturing your friends with.  Really, what more could you ask?</p>

<p><script>AddToCart("eights");</script></p>]]></description>
         <link>http://www.pavelspuzzles.com/2010/11/easy_eight_hard_eight.html</link>
         <guid>http://www.pavelspuzzles.com/2010/11/easy_eight_hard_eight.html</guid>
         <category>Mechanical puzzles</category>
         <pubDate>Tue, 23 Nov 2010 22:03:24 -0800</pubDate>
      </item>
            <item>
         <title>The Cruciatus Curse</title>
         <description><![CDATA[<p>Each year, we begin the planning process for the Microsoft Intern Puzzleday in the same way, with an evening of training in puzzle design.  This is primarily aimed at the folks who've never helped put on such an event before, but it's a good refresher for everyone.  The best part, though, comes after our training lead, Kenny Young, works through his PowerPoint slides.  At that point, we break up the group into smaller sections of 5-8 people each, and each section does some slightly directed brainstorming on puzzle ideas.  Not only does this help the newbies get a sense of how the process works, and provides a safe environment for tossing out ideas, but we often get three or four puzzles from this that survive all the way to the final event.</p>

<p>I said "slightly directed" brainstorming, and that describes it pretty well.  Each section gets a brief visit from Kenny, who imparts a little germ of an idea to kick things off.  My first year, the theme of the event was to be Hogwarts, the school for wizards from the Harry Potter books.  Kenny came to our section and looked a little sheepish.</p>

<div class="product-image-right">
  <script>PopUpPDF("cruciatus");</script>
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<p>"Um, this is going to be pretty sketchy, even moreso than usual; I'm sorry about that, but I'm also sure you'll be able to do <em>something</em> with it."</p>

<p>Oh goodie, I thought; this should be good.</p>

<p>"OK, Hogwarts is in England, right?  Well, I've noticed that the British seem to have a lot of interesting <em>pairs</em> of things.  For example, Marks & Spencer, the department store in London.  Or bangers and mash, which is apparently something you can eat.  Got it?"</p>

<p>We all stared at him.</p>

<p>"Well, that's it.  Go for it!"  And then he left, presumably to go torture the next section, too.</p>

<p>As I said, the brainstorming is only "slightly" directed.</p>

<p>As a kind of temporizing maneuver, we first spent some time trying to come up with a bunch more such "pairs".  After a while of that, the ideas started flowing for how to make use of them.  Over the course of the next half hour or so, we played around with a lot of ideas, but just one of them had any staying power, and Cruciatus Curse was the result.  The actual detailed puzzle design work was a collaboration between me and Stacey Eck, but we probably wouldn't have gotten that far without all of the ideas flowing around that initial brainstorming session.</p>

<p>The answer to Cruciatus Curse, like all of the puzzles in Puzzleday, is a single word or short phrase.</p>

<p>Well, that's it.  Go for it!</p>]]></description>
         <link>http://www.pavelspuzzles.com/2010/08/the_cruciatus_curse.html</link>
         <guid>http://www.pavelspuzzles.com/2010/08/the_cruciatus_curse.html</guid>
         <category>Microsoft Intern Puzzleday</category>
         <pubDate>Mon, 23 Aug 2010 21:39:18 -0800</pubDate>
      </item>
            <item>
         <title>The Calibron 12-Block Puzzle</title>
         <description><![CDATA[<div class="product-image-left">
<script>PopUpProduct("calibron-perspective-ad-1932");</script>
</div>

<p>In March of 1931, a man named <a href="http://en.wikipedia.org/wiki/Theodore_Edison">Theodore Edison</a>, younger son of the famous inventor Thomas Alva Edison, <a href="http://books.google.com/books?id=BGr0rrClKCAC&pg=PA404&dq=%22calibron+products%22&hl=en&ei=O8lwTP3QNoi6sQOlgIGKCw&sa=X&oi=book_result&ct=result&resnum=5&ved=0CD8Q6AEwBDgK#v=onepage&q=%22calibron%20products%22&f=false">filed articles of incorporation</a> for a company named <em>Calibron Products</em> in West Orange, New Jersey.  The company's first product was a<a href="http://books.google.com/books?id=4CcDAAAAMBAJ&pg=PA111&dq=%22calibron+products%22&hl=en&ei=O8lwTP3QNoi6sQOlgIGKCw&sa=X&oi=book_result&ct=result&resnum=1&ved=0CCoQ6AEwADgK"> special kind of graph paper</a>, designed to make it easier to create perspective drawings.</p>

<div class="product-image-right">
<script>PopUpProduct("calibron-ad-1935");</script>
</div>

<p>But in December of the next year, the company <a href="http://books.google.com/books?id=SVxbAAAAIAAJ&pg=PA10&lpg=PA10&dq=%2Bcalibron+1932&source=bl&ots=djd_sM0iPJ&sig=n8OptONl94Ab_4HxA0UHsbA8N-8&hl=en&ei=0sZwTLWBMInWtQP72JC_Cw&sa=X&oi=book_result&ct=result&resnum=1&ved=0CBIQ6AEwAA#v=onepage&q=%20calibron%201932&f=false">filed for a copyright</a> on "The Calibron 12-Block Puzzle".  An advertisement for the puzzle appeared a few years later, in the <a href="http://books.google.com/books?id=lyoDAAAAMBAJ&pg=PA93&lpg=PA93&dq=calibron+puzzle&source=bl&ots=BoM4JfT8vW&sig=Y2-uIJCEXk66hE7zUQzb-UzGnnY&hl=en&ei=CcRwTIKtE4KcsQO6p-29Cw&sa=X&oi=book_result&ct=result&resnum=3&ved=0CBwQ6AEwAg#v=onepage&q&f=false">January 1935 issue of Popular Science magazine</a>.</p>

<p>The <a href="http://home.comcast.net/~stegmann/assembly.htm#calibron">instructions for the puzzle</a> read, in part, "The problem is to arrange the twelve blocks to form a single large rectangle. Any rectangle will do, provided that all twelve blocks are used... We guarantee that there is a straightforward, accurate solution of this puzzle in a single plane, and without recourse to any kind of trick... However, in spite of the enormous number of possibilities, there appears to be only one basic arrangement which satisfies the above conditions... We once offered $25 for the first solution of this problem and distributed hundreds of puzzles at that time, but received almost no correct arrangements! We should like to hear from you if you succeed in making the rectangle unaided."</p>

<p>Not very many people have copies of the <a href="http://www.puzzlein.com/museum/puttogether/twelveblocks.html">original Calibron 12-Block Puzzle</a>, and that bothered a good customer of mine, who wrote me earlier this year asking for advice on how to get a few copies of the puzzle made.  I decided to make the copies for him myself, and once the first prototype came off the laser cutter, I decided that it was quite an intriguing design, and that I'd like to make it more widely available again.</p>

<div class="product-image-right">
<script>PopUpProduct("calibron");</script>
</div>

<p>The twelve rectangles making up the puzzle have very promising dimensions, with lots of obvious interrelationships that lead you to think that won't have too much trouble getting them to fit together in nice ways, and that's true, as far as it goes.  However, "as far as it goes" isn't likely to be as far as actually solving the puzzle unless you put in some time and concentration.  This is one of those very attractive puzzles that just won't yield without a bit of a fight.</p>

<p>With modern computers, it was straightforward to verify the original marketing claim: there is, indeed, a unique solution to the puzzle.  I think you'll enjoy torturing your friends as they try to find it.</p>

<p><script>AddToCart("calibron");</script></p>]]></description>
         <link>http://www.pavelspuzzles.com/2010/08/the_calibron_12block_puzzle.html</link>
         <guid>http://www.pavelspuzzles.com/2010/08/the_calibron_12block_puzzle.html</guid>
         <category>Mechanical puzzles</category>
         <pubDate>Sat, 21 Aug 2010 17:25:27 -0800</pubDate>
      </item>
            <item>
         <title>Square Dance</title>
         <description><![CDATA[<p>Take a 2x2 square, and join it to another 2x2 square, but only by <em>half</em> an edge.  There's only one way to do that (ignoring reflections and rotations), shown below:<br />
<center><br />
<img src="/images/two-squares.jpg"><br />
</center><br />
Now join on a third 2x2 square, again by only half an edge.  This time, there are just four possibilities, all seen in the photograph below.</p>

<div class="product-image-right">
<script>PopUpProduct("square-dance");</script>
</div>

<p>Back in 2002, my good friend <a href="http://www.obsessionwithfood.com/">Derrick Schneider</a> noticed this nice little set of slightly strange shapes and wondered whether or not they'd make a good puzzle.  He <a href="http://programmingobsession.blogspot.com/">whipped up</a> 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!</p>

<p>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.</p>

<p>Perhaps that explains why, when Derrick presented his puzzle at the 22nd annual <a href="http://www.pavelspuzzles.com/2005/07/hello_from_helsinki.html">International Puzzle Party</a>, the jury for the <a href="http://www.johnrausch.com/DesignCompetition/2002/results.htm">Puzzle Design Competition</a> awarded it an Honorable Mention, one of just three puzzles so honored.</p>

<p>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.</p>

<p><script>AddToCart("square-dance");</script></p>]]></description>
         <link>http://www.pavelspuzzles.com/2010/08/square_dance.html</link>
         <guid>http://www.pavelspuzzles.com/2010/08/square_dance.html</guid>
         <category>Mechanical puzzles</category>
         <pubDate>Sat, 21 Aug 2010 16:25:56 -0800</pubDate>
      </item>
            <item>
         <title>Anansi&apos;s Maze</title>
         <description><![CDATA[<p>As I write this, I'm helping to host the first Microsoft <u>Non</u>-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.)</p>

<div class="product-image-right">
<script>PopUpProduct("anansi");</script>
</div>

<p>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.</p>

<p>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.</p>

<p>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.</p>

<p>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?</p>

<p><script>AddToCart("anansi");</script></p>]]></description>
         <link>http://www.pavelspuzzles.com/2009/08/anansis_maze.html</link>
         <guid>http://www.pavelspuzzles.com/2009/08/anansis_maze.html</guid>
         <category>International Puzzle Party (IPP)</category>
         <pubDate>Wed, 05 Aug 2009 18:32:52 -0800</pubDate>
      </item>
            <item>
         <title>Crystal Ball</title>
         <description><![CDATA[<p>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 <a href="http://www.pavelspuzzles.com/2008/05/octamaze.html">Octamaze</a> and <a href="http://www.pavelspuzzles.com/2009/08/gamesters_of_triskelion.html">Gamesters of Triskelion</a> puzzles came out of this realm, and for my <a href="http://www.pavelspuzzles.com/2005/07/hello_from_helsinki.html">IPP</a> 2008 <a href="http://www.pavelspuzzles.com/2005/07/ipp_25_puzzle_exchange.html">Exchange</a> puzzle, I wanted to move up from the octahedron to my favorite of the <a href="http://en.wikipedia.org/wiki/Platonic_solids">Platonic solids</a>, the <a href="http://en.wikipedia.org/wiki/Dodecahedron">dodecahedron</a>.  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.</p>

<div class="product-image-right">
<script>PopUpProduct("crystal-2");</script>
</div>
<div class="product-image-right">
<script>PopUpProduct("crystal");</script>
</div>

<p>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.)</p>

<p>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.</p>

<p><!--<br />
The final piece of the design came from my realization, late at night while trying to fall asleep, that there was a wonderful pun opportunity in naming the puzzle, since IPP last year was held in Prague.  Once I'd come up with the name "<a href="http://en.wikipedia.org/wiki/Star_Trek">Star Czech</a>", and stifled my giggles to avoid waking up my wife, I knew I was done.<br />
--></p>

<p>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.</p>

<p>[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... :-)]</p>

<p><script>AddToCart("crystal");</script></p>]]></description>
         <link>http://www.pavelspuzzles.com/2009/08/star_czech.html</link>
         <guid>http://www.pavelspuzzles.com/2009/08/star_czech.html</guid>
         <category>International Puzzle Party (IPP)</category>
         <pubDate>Wed, 05 Aug 2009 17:21:44 -0800</pubDate>
      </item>
            <item>
         <title>Gamesters of Triskelion</title>
         <description><![CDATA[<p>My orignal plan, when designing the <a href="http://www.pavelspuzzles.com/2008/05/octamaze.html">Octamaze</a> puzzle, was that it would serve double duty, being both my gift to everyone at Gathering for Gardner 8 and something to torture the interns with at the 2008 <a href="http://www.pavelspuzzles.com/microsoft_intern_puzzleday/">Microsoft Intern Puzzleday</a>.  Sadly, though, it became quite clear during initial playtesting that Octamaze would be too difficult for the intern event.  (I was willing to make the mathematicians, puzzlers, and magicians at G4G8 work harder...)</p>

<div class="product-image-right">
<script>PopUpProduct("triskelion");</script>
</div>

<p>Still, I thought I could at least reuse the primary mechanical idea of Octamaze, and so I started from there when designing the Gamesters of Triskelion puzzle; I did, though, make that part a bit easier.  The 2008 Puzzleday theme, for those of you who didn't recognize it immediately from the title, was Space, including many science-fiction references.  I was put in mind of the <a href="http://en.wikipedia.org/wiki/Gamesters_of_Triskelion">Gamesters of Triskelion</a> episode from the original Star Trek series by the triangular shape of the pieces from Octamaze, and somehow it occurred to me to check whether or not "triskelion" was actually a normal English word.  As it happens, it is: a <a href="http://en.wikipedia.org/wiki/Triskelion">triskelion</a> is a (sometimes quite literally) three-legged motif from heraldry and graphic design.  I particularly liked some of the more modern interpretations of the motif, so I incorporated one into the etching on the pieces.</p>

<p>Gamesters of Triskelion is the third in my series of <a href="http://www.pavelspuzzles.com/multistage_puzzles/">multi-stage puzzles</a>, where solving one stage of the puzzle creates another puzzle for you to solve, on through some number of stages until you reach a single-word or short-phrase final answer.  I'm having a lot of fun designing such puzzles, so you can expect the series to continue for quite a while.</p>

<p>Unlike most of my puzzles, this one comes with some "flavor text", not <i>essential</i> to solving the puzzle, but perhaps helpful:<br />
<blockquote><br />
Captain's log, stardate 3211.9: We are leaving starsystem M-24 Alpha, having convinced the three disembodied Providers, the one-time Gamesters of Triskelion, to help their former gladiators to form a new, free civilization.  This should end the deadly gambling in their obsessively triangular fighting arena.</p>

<p>As we left orbit, the Providers transported a small octahedron onto the bridge, along with an engraved tablet (three sided, of course) in what appears to be their language.  During transport, the faces of the octahedron detached from one another, so now we have eight triangular pieces.</p>

<p>Spock believes it will be straightforward to reassemble them since, he says, they can only fit together in one way.  He is more puzzled about the meaning of the etchings on the faces, and how they might relate to the tablet, but assumes that this will become clear once the octahedron is back together.<br />
</blockquote></p>

<p><script>AddToCart("triskelion");</script></p>]]></description>
         <link>http://www.pavelspuzzles.com/2009/08/gamesters_of_triskelion.html</link>
         <guid>http://www.pavelspuzzles.com/2009/08/gamesters_of_triskelion.html</guid>
         <category>Microsoft Intern Puzzleday</category>
         <pubDate>Wed, 05 Aug 2009 09:57:00 -0800</pubDate>
      </item>
            <item>
         <title>On Looking at Puzzle Solutions</title>
         <description><![CDATA[<p>Over on my posting about the <a href="http://www.pavelspuzzles.com/2007/08/the_devils_half_doven_1.html">Devil's Half Doven</a> puzzle, Jon Acord posted a comment in which he said, "I never look at the solutions. Should I?".  My reply to that question got so long, I decided I might as well turn it into a full blog posting.</p>

<p>I think the answer depends on the puzzle. Some puzzles are "aha!" events: you have some blazing insight and then all is clear (and sometimes you feel like a dummy for not having seen it earlier).  If you look at the solution for one of these, it's all or nothing: you won't get just a little information on the path, you'll be spoiled on that puzzle forever, because the insight is usually quite memorable.  My <a href="http://www.pavelspuzzles.com/2007/08/sleazier_1.html">Sleazier</a> puzzle most closely fits into this category.</p>

<p>Some other puzzles are "search" puzzles, where you're just going to have to try a lot of combinations and, over time, try to learn something about the "texture" of the search space that allows you (a) to sharply reduce the amount of effort required, and (b) to make your search systematic, so you won't miss the solution. (<a href="http://www.pavelspuzzles.com/2007/08/the_devils_half_doven_1.html">Doven</a> falls into this category.) Often, you can look at the solution for a search puzzle (or, better, have someone else look at it) and get a hint or two in the form of a restriction in the search space; for example, "that piece goes there", or "this piece fits into that one". Of course, you can choose how many such hints/restrictions you give yourself before finishing the solve yourself.</p>

<p>Finally, there are multi-layered puzzles, in which each layer falls into one of the two categories above. (My <a href="http://www.pavelspuzzles.com/2008/05/octamaze.html">Octamaze</a> and <a href="http://www.pavelspuzzles.com/2007/08/the_ooo_tray_1.html">Ooo Tray</a> puzzles are like this.) Here, you can look at the solution (or, again, get someone else to look) and get a hint on just one layer, leaving the rest still available for solving.</p>

<p>Octamaze has more layers than people expect, so I wrote up a <a href="http://www.pavelspuzzles.com/g4g8">detailed walkthrough</a> that doesn't put too much information on any one web page, to allow just such an incremental hinting approach.<br />
</p>]]></description>
         <link>http://www.pavelspuzzles.com/2008/07/on_looking_at_puzzle_solutions.html</link>
         <guid>http://www.pavelspuzzles.com/2008/07/on_looking_at_puzzle_solutions.html</guid>
         <category>Puzzle Philosophy</category>
         <pubDate>Thu, 03 Jul 2008 11:48:44 -0800</pubDate>
      </item>
            <item>
         <title>Octamaze</title>
         <description><![CDATA[<p>Back in 1994, some folks decided it would be a cool idea to give a special 80th birthday present to <a href="http://en.wikipedia.org/wiki/Martin_gardner">Martin Gardner</a>, long-time author of the very popular and significant Mathematical Games column in <a href="http://www.sciam.com/">Scientific American</a> magazine, as well as many books of mathematical puzzles and articles.</p>

<p>What better way to mark the occasion, they thought, than to bring together a lot of people who had enjoyed, and been influenced by, Martin's work?  So they invited a bunch of people from the fields nearest to Martin's heart, from mathematics, puzzling, and stage magic, to come to Atlanta for the "Gathering for Gardner": several days of talks, performances, and exhibitions in celebration of Martin's 80th birthday.  That first Gathering was such a huge success that the organizers decided to keep doing it and, every two years since then, there's been a Gathering.</p>

<p>I've known about the Gathering for some time now, through contacts at the <a href="http://www.pavelspuzzles.com/2005/07/hello_from_helsinki.html">International Puzzle Party</a>, but I was pleased to be invited for the first time this year, for "Gathering for Gardner 8", or "G4G8".  Similar to the <a href="http://www.pavelspuzzles.com/2005/07/ipp_25_puzzle_exchange.html">Puzzle Exchange</a> every year at IPP, the organizers of the Gathering ask that everyone provide a gift of some sort for all of the other participants.  Many people fulfill this obligation by giving a talk and writing up a short article for the conference proceedings book, but many others bring puzzles, magic tricks, or other entertaining objects.</p>

<p>You know, of course, what I did, right?</p>

<div class="product-image-right">
<script>PopUpProduct("octamaze");</script>
</div>

<p>Every Gathering for Gardner has a theme; I think you may be able to guess what all of the previous themes were when I tell you that this year's was "8, or the crazy lazy 8 (infinity)".  I wanted to bring a new puzzle design that would strongly incorporate the theme, of course, but I also wanted to continue down the path I'd forged with my <a href="http://www.pavelspuzzles.com/2007/08/the_ooo_tray_1.html">Ooo Tray</a> puzzle last year.  I wanted to design another multi-stage puzzle, with each solving stage revealing clues to the next stage, culminating in a "final answer" that was somehow satisfying.</p>

<p>I'd been idly thinking about three-dimensional edge-matching puzzles for a while (What?  Don't try to tell me you don't think about such things, too.), and I'd wondered if it would work to make a polyhedron where the sides fit together with tabs and slots.  With a theme like "8", this was a perfect (some might say Platonic) opportunity!</p>

<p>A little software work and many design iterations later, Octamaze was born.  There are at least four stages in solving this puzzle, providing a good hour or two of "play time".  If you buy a copy of Octamaze and get stuck, I've created a sequence of web pages giving a progression of <a href="http://www.pavelspuzzles.com/g4g8">hints for solving it</a>.  (Don't worry: clicking on that link won't immediately reveal any spoilers.  If you keep clicking on the links at the bottom of each page, though, you'll eventually see all of Octamaze's secrets, so be careful.)</p>

<p><script>AddToCart("octamaze");</script></p>]]></description>
         <link>http://www.pavelspuzzles.com/2008/05/octamaze.html</link>
         <guid>http://www.pavelspuzzles.com/2008/05/octamaze.html</guid>
         <category>Mechanical puzzles</category>
         <pubDate>Sun, 04 May 2008 22:18:27 -0800</pubDate>
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