Difference between revisions of "Tom's move"
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Red's main group by double threat at the cells marked "*". Note that 2 and 3 do not actually need to be played; these moves have been included for clarity. | Red's main group by double threat at the cells marked "*". Note that 2 and 3 do not actually need to be played; these moves have been included for clarity. | ||
Revision as of 08:07, 23 September 2021
Contents
Introduction
Tom's move is a trick that enables a player to make a connection from a 2nd-and-4th row parallel ladder. It can also be used to break through a 2nd row ladder using a single stone on the 4th row, or to connect a single stone on the 4th row to the edge. Its name originates from Tom Ace (player Tom239), who devised it during a game against dj11, on 15 December 2002 on Playsite. This was not its first use ever, just how it came to be known among Hex players on Playsite.
Description
Suppose Red has a 2nd-and-4th row parallel ladder and the amount of space shown here:
Then Red can connect by playing at "*", the so-called "Tom's move".
Usage examples
Connecting a 2nd row ladder using an isolated stone on the 4th row
Red to move and win:
The solution is to push the ladder to 3 and then play Tom's move:
A single stone on the 4th row is connected
Consider a single stone on the 4th row, with the amount of space shown:
Then Red can connect as follows:
Red squeezes through the bottleneck at 2, starts a 2nd row ladder at 4, then plays Tom's move at 6. Note that all of Blue's moves are forced; if Blue plays differently, Red connects outright.
In a game
Red to move:
Red's d4 group is already connected to the top edge by edge template IV1-a. To connect to the bottom, Red plays as follows:
Now Red is connected by Tom's move. Note that d8 is already connected to Red's group by double threat at c8 and d9.
Why Tom's move is connected
We start with two red threats:
These leave only blue moves in the ziggurat.
If Blue plays there other than at a, then Red plays at a.
In that case, Red's 2 connects back via either of the cells marked "*", and since the piece Blue just played is in only one of the x,y,z regions, Red's 2 also connects down via either of the remaining two of those three regions.
Thus Blue's only remaining hope is to play at a.
Red responds like this:
Red's 4 is now connected to the bottom via edge template IV2b, and to Red's main group by double threat at the cells marked "*". Note that 2 and 3 do not actually need to be played; these moves have been included for clarity.
Variants
Tom's move also works when the hex marked "a" is not empty, provided that "b" connects to Red's main group.
For example, Tom's move works in this situation:
