Difference between revisions of "Tom's move"

Revision as of 20:09, 11 September 2021

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 red2,

then Red plays red2. In that case, red2 connects back via either "*", and since the piece Blue just played is in only 1 of the x,y,z regions, red2 also connects down via either of the remaining 2 of those 3 regions. Thus Blue's only remaining hope is to play at red2.

Red responds like this:

red4 is now connected to the bottom via edge template III2-b, 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:

See also

• 2nd and 4th row parallel ladder escape