The Gap is one of my favorite openings because it creates such a dynamic situation in the center of the board. It can be played by first player, second player, or both, and I’m not even sure I know of all the best responses. Let’s look at the opening, talk about what it does, then go over two responses.
First player opens with a standard horizontal wall in the middle. If Purple mirrors, Green can disrupt Purple’s horizontal line with a second wall that leaves a one space gap near the center. This wall also forces 2 more single spaced gaps. The gap in the center takes 3 walls to close, while the two near the edges both take 2 walls to close.
Some of our readers may remember seeing this opening in our post about responses to mirror play. Here we see it in a few more forms.
Following Green’s gap, Purple can continue the mirror with a gap of his own. This is one of my favorite opening boards. I’ve hardly had a chance to explore all of the possibilities. I’m not even sure which player has the advantage at this point.
And a third variation, instead of trying to mirror Green’s first wall, Purple goes on the attack and plays a gap right off the first move. This variation feels a bit risky to me. It places 2 walls in front of you (as second player) without any defense. While I feel like this opening benefits first player, I’ve been victim to it a number of times now
What can you do to respond to the gap? Lets look at the third variation again and explore Green’s position.
The gap creates all sorts of problems. First the horizontal line is three spaces from Green’s goal, so 2 walls will be needed to close the back and avoid being sent around. Second, either direction Green chooses to move towards he will have a gap to his rear. The right side of the board is more attractive than the left because it leaves Green with only one gap to his back.
Because of this I think the strongest response is to push to the right. This leaves Purple in a difficult position. Move left and Green can close the side with 2 walls. Move right and Green already has the wall advantage pushing top. On the other hand Green’s vertical wall creates a vertical line that Purple can use to close his rear in 2 moves, preventing Green from sending him around. So while this response is safe for Green, it does make it harder for Green to attack, and it does leave a gap to Green’s rear that might have to be closed.
A second response is to control the center gap. A horizontal wall behind the initial horizontal line allows the player to place a second vertical wall pushing in either direction. If the opponent tries to place this vertical wall and choose the direction, Green then has the option to close with a third wall. This is a defensive response, but seeing as Purple’s side of the board is wide open, I don’t think it weakens any future attacks.
Do you play the gap opening? I’d love to hear our reader’s thoughts on what the best responses are.
Screenshots from Martijn’s Quoridor App.