Tetris was invented by Russian mathematician Alexey Pajitnov. He was inspired by Solomon Golomb's game of Pentominos, popularized in Martin Gardner's Mathematical Games column in Scientific American. Pentominos are the twelve shapes that can be made by joining five squares edge to edge. There are hundreds of games you can play with pentominoes, starting with fitting the twelve shapes into a solid rectangle.

Alexey turned Pentominoes into a dynamic computer game by having the player fit blocks together in real time as they fall. He reduced the number of squares from five to four, yielding the seven Tetris pieces (that's five distinct shapes, plus two asymmetric mirror images). "Tetris," by the way, is Greek for "four".

Most importantly he introduced the rule that if you form a solid horizontal row of square blocks, the row disappears and all blocks above move down a row. This behavior would be impossible in a physical puzzle, but is perfectly natural in the computer medium. This sort of innovation is what excites me most about computer games: finding ways to go beyond what you can do in the physical world.

I first met Alexey in the early 90s at the Game Developers Conference. Over the years we have gotten to know each other, giving talks together on puzzle game design at the Game Developers Conference. Alexey now works at Microsoft, where he has designed several wonderful CD-ROM computer puzzle games, including the award winning Pandora's Box (a sumptuously illustrated collection of hundreds of puzzles, all variations on jigsaw puzzles).

Alexey maintains a connection with Tetris through his longtime colleague Henk Rogers, the man who keeps the Tetris franchise flourishing through his game development company Blue Planet Software in San Francisco. By now Tetris has been ported to virtually every gaming platform, even including a tiny keychain version. Over 50 million copies have been distributed, making it the most popular electronic game of all time. Henk likes to call Tetris the first computer sport -- a game so popular that it has become a global standard.

Blue Planet continues to spin new variations on the Tetris theme. One recent incarnation is The Next Tetris, for which I designed several dozen puzzles. In TNT, as it is known, the standard Tetris piece shapes are composed of smaller pieces which can fall apart on impact. When you clear a line it can trigger a cascade in which parts of pieces fall to fill in holes, in turn clearing more lines. Cascades make TNT strategy deeper and harder to predict than in conventional Tetris. You can read about how I designed the TNT puzzles in slides from my talk at the 2000 Game Developers Conference.

Here's what I like about Tetris.

• Simple. The whole game can be played with four buttons. Graphics are so simple the keychain version uses a 9 by 12 pixel display.
• Deep strategy. Complexity comes out of the state of the board: the position of every block on the screen matters.
• Native to computer medium. Unlike Solitaire and Minesweeper, Tetris is not a copy of a physical game.
• Spectator sport. Tetris is fun to watch. You can learn how to play by watching for a minute or two
• Constructive. Like SimCity and The Incredible Machine, Tetris is about building, not destroying.
• Rhythm. When Alexey designs a game he focuses on getting the rhythm right. Tetris has the quick rhythm of positioning a falling piece, and the slow rhythm of clearing lines -- it engages you on all time scales.

The Tetris rules are so good they have an air of inevitability, like the laws of physics. You can make the game different, but it's hard to make it better. So what has Blue Planet done to make sequels?

• Layer on new rules. Instead of changing the rules, keep the original rules and additional goals. Maintaining the original rules means experienced players can keep using everything they know.
• Unify different versions. Different implementations of Tetris have subtly different rules for how pieces turn. Henk unified the Tetris universe by creating a turning rule that subsumes all other rules. No matter which implementation you have played before, you won't be surprised. Most players won't notice the innovation...and that's the point.
• Sprint mode. The original Tetris is an exhausting marathon: play till you drop. In the end you always fail and the game takes a long time to play. New versions of TNT add a sprint mode in which you try to get the best score within a short fixed time.
• Kid's Tetris. Despite its simplicity, Tetris isn't actually that easy to learn. Experienced players tend to want more complexity, but Henk was wise enough to recognize the need for a simpler version.
• Cascades. A thrilling moment in any game is when one move triggers a chain reaction of consequences. TNT adds cascades to Tetris. Experts love it, but beginners find it harder to learn.

WHAT’S NEW JUNE 2001

Inversion of the Month: Termes (artist who paints panoramas on spheres).

Discover Magazine Boggler
May: Three puzzles that involve counting: The Toothpick Tally (how many squares or triangles are in these figures), Don't Count that Dial! (how many phone numbers are possible), Counting on Your Fingers (how high can you go?).
June: Three puzzle about voting: Electoral Confusion (based on the electoral college fiasco in the recent US presidential elections), Flavor Face-Off (paradoxes in voting methods), and Tennis Mismatch (how to schedule a fair tennis tournament).

Talks: Designing Web Games that Make Business Sense, and Building Web Games in Flash
For the Game Developers Conference, Mar 20-24, San Jose, California. Download the PowerPoint slides or read the papers.

FROM READERS

Dick Termes is an artist in South Dakota who has explored the art of painting on spheres. The original spheres are expensive, but he has affordable paper models for sale as well as a video. I originally met Dick at an Art Math conference.

Slavik Jablan. Speaking of art and math, Slavik Jablan edits an online journal called Visual Mathematics. See the latest issue at:

Mark Yates is a geometry teacher in Chattanooga TN who uses my inversions in his class. Here is his page of sites about symmetry:

Ivan Skvarca created a beautiful puzzle site en Español. Here his original inversions. I especially like the inversion on LUZ (light), which has an ingenious interpretation of cursive Z.

Roger, a new member of my puzzle designers emailing list, has compiled a wonderful list of puzzle sites.

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