Editing Domineering (section)

==Basic examples==

===Single box===
Other than the empty game, where there is no grid, the simplest game is a single box.

[[Image:20x20square.png]]

In this game, clearly, neither player can move. Since it is a second-player win, it is therefore a [[zero game]].

===Horizontal rows===
[[Image:20x20square.png]][[Image:20x20square.png]]

This game is a 2-by-1 grid.  There is a convention of assigning the game a [[positive number]] when Left is winning and a [[negative number|negative]] one when Right is winning. In this case, Left has no moves, while Right can play a domino to cover the entire board, leaving nothing, which is clearly a zero game. Thus in [[surreal number]] notation, this game is <nowiki>{|</nowiki>0} = −1. This makes sense, as this grid is a 1-move advantage for Right.

[[Image:20x20square.png]][[Image:20x20square.png]][[Image:20x20square.png]]

This game is also <nowiki>{|</nowiki>0} = −1, because a single box is unplayable.

[[Image:20x20square.png]][[Image:20x20square.png]][[Image:20x20square.png]][[Image:20x20square.png]]

This grid is the first case of a choice. Right ''could'' play the left two boxes, leaving −1. The rightmost boxes leave −1 as well. He could also play the middle two boxes, leaving two single boxes. This option leaves 0+0 = 0. Thus this game can be expressed as <nowiki>{|</nowiki>0,−1}. This is −2. If this game is played in conjunction with other games, this is two free moves for Right.

====Vertical rows====
Vertical columns are evaluated in the same way. If there is a row of 2''n'' or 2''n''+1 boxes, it counts as −''n''. A column of such size counts as +''n''.

===More complex grids===
[[Image:20x20square.png]][[Image:20x20square.png]]<br>
[[Image:20x20square.png]][[Image:20x20square.png]]

This is a more complex game. If Left goes first, either move leaves a 1×2 grid, which is +1. Right, on the other hand, can move to −1. Thus the [[surreal number]] notation is {1|−1}.  However, this is not a surreal number because 1 > −1. This is a Game but not a number. The notation for this is ±1, and it is a [[hot game]], because each player wants to move here.

[[Image:20x20square.png]][[Image:20x20square.png]][[Image:20x20square.png]]<br>
[[Image:20x20square.png]][[Image:20x20square.png]][[Image:20x20square.png]]

This is a 2×3 grid, which is even more complex, but, just like any Domineering game, it can be broken down by looking at what the various moves for Left and Right are. Left can take the left column (or, equivalently, the right column) and move to ±1, but it is clearly a better idea to split the middle, leaving two separate games, each worth +1. Thus Left's best move is to +2. Right has four "different" moves, but they all leave the following shape in some [[rotation]]:

[[Image:20x20square.png]][[Image:20x20square.png]][[Image:20x20square.png]]<br>
[[Image:20x20square.png]]

This game is not a hot game (also called a [[cold game]]), because each move hurts the player making it, as we can see by examining the moves. Left can move to −1, Right can move to 0 or +1. Thus this game is {−1|0,1} = {−1|0} = −{{frac|1|2}}.

Our 2×3 grid, then, is {2|−{{frac|1|2}}}, which can also be represented by the mean value, {{frac|3|4}}, together with the bonus for moving (the "temperature"), {{frac|1|1|4}}, thus: <math>\textstyle\left\{2 \left| -\frac{1}{2}\right.\right\} = \frac{3}{4} \pm \frac{5}{4}</math>