# Equipotential Chess III

Last updated 2020-03-06 11:18:10 SGT

After 4 years of no updates, I am proud to announce the release of an official 3-player variant of equipotential chess:

The ruleset for the 3-player variant is largely based off my favourite 3-player xiangqi variant, which is 三国棋 ("the game of the Three Kingdoms"). Just as 象棋 plays to the legends surrounding the 楚汉相霸, this variant plays to the tropes of 三国演义. I can personally vouch for the amount of drama it has the potential to generate among close friends playing it. Where 象棋 is deep, 三国棋 is strategically chaotic owing to the nontrivial game theory changes from the introduction of a third player — collusion and betrayal abound. I just had to ruin it all by putting it in space.

One nontrivial property of this variant (both in the canonical form and in my equipotential variant) is that the central file of the map has an interesting topology: it is Y-shaped, connecting all three kingdoms, so that e.g. in principle all three generals can threaten each other via 飞将 at the same time. In the equipotential scenario, this is implemented by connecting all three point sources through the central saddle point (in addition to permitting the usual geometric path up the field line).

Additionally, capturing a general is possible, since the threatened side may not be able to react in time to prevent capture in event of a coordinated attack from the two other players. Alternatively, a player may be placed in a stalemate in the usual fashion, and be forced to resign; these outcomes do not necessarily end the game. Instead, the vanquisher claims the first loser's remaining pieces and must still defeat the remaining opponent to actually claim victory. To prolong the game further, optional "bannerman" pieces, acting in a similar fashion to the usual 马 pieces (with accompanying 顶马脚 variant rules) may also be employed — where 马 move one ordinary space and one diagonal step, the bannermen move two spaces before the diagonal step, and (in my implementation) can be blocked by any piece placed on both these spaces.

As usual, the game can be found in the usual place at https://gitlab.com/darthoctopus/equipotential. I welcome feedback of all kinds.

### Changelog

• 3 Player variant board (change back to 2 players by editing the variable PLAYERS in the file equipotential/config.py)
• Significant engine changes to accommodate new 3-player ruleset; the code is now generalisable to an arbitrary number of players
• Bug fixes for 兵 movement
• Press number keys to resign and K to skip (needed for 3-player variant to resolve stalemates)
• 兵_FLAG: control whether the 兵 may move between an enemy point source and the first equipotential
• EXTRA_兵: extra 兵 to maybe pad out the overpowered 中炮 strategy
• OPT_PIECES: bannermen pieces in 3-player variant