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Half-open vs open

Posted by nand on June 6, 2009

I like developing terminology for games. (It’s always a kick when people start using terms you devised. I was pleased to see Will Shortz referring to “cages” in a puzzle recently — it’s a term I coined for killer sudoku a few years ago, & seems to have stuck.) & more importantly, having terms for things can advance your understanding of a game. (I will post at some point about the idea of the “semi-mirror” for instance.) So: I’d like to refine the usual classification of openings into “open” and “closed” into a three-way distinction.

  1. “closed”: the most popular kind: violet’s 2nd move creates a 1-square hole (what I call an “eye”). XF Rubik and Yasu, discussed in previous posts, are examples. (POTENTIAL VARIANT: violet creates an i2 hole or larger. I have yet to see an opening that does this that is very effective.)
  2. “open”: violet creates no eye, offering orange the chance to wrap around on move 2 and actually pass through on move 3.
  3. “half-open”: violet creates no eye, but positions the 2nd piece in such a fashion that orange cannot immediately penetrate; it will take until move 4 to actually pass through violet’s piece-formation.

Here are four examples of half-open openings.

Note that orange cannot play directly into the central hole on move 2; it will take 3 moves to reach it, and (if orange wishes to do so, & violet does not obstruct him) a 4th move to actually pass through the hole. — Also note that in all these openings it is very difficult for violet BOTH to attack AND to defend the hole, because it’s very easy for violet to end up in a situation where the 1 piece is the only way to block the central leak.

My general instinct is that this is a fairly dodgy way for violet to open, but having lost plenty of games to these as orange I cannot say this for sure yet. The basic question with all of these is whether orange should play on the left or right on move 2. Typically on the right the response is Y upright, threatening to either wrap round the top or play Z5 into the central hole; typically on the left the response is W or F wrapping around, planning to put a piece in the central hole on move 3. Further investigations pending…


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