Power Mover

Introduction

After we proposed SC-chess, a variant of Hostage chess with self-capture, we utilize the feature of self-capture for promotion of several pieces. Power mover is a variant of SC-chess. Besides pawn promotion, we allow promotion of a rook, bishop, and knight.

A rook is promoted to an empress, moving like a rook or a knight, a bishop to a queen, and a knight to a princess, moving like a knight or a bishop. They are not only promoted but also demoted, switched between two levels again and again with certain rules.

Setup

We use the ordinary initial arrangement of ordinary chess pieces on an ordinary chess board. Like Hostage chess or SC-chess, both sides of each player are assigned to rooms for reserve pieces, your right side is a prison for your opponent's pieces, and left side is an airfield for your pieces.

Promotion Rules

Rules of the game are the same as ones of SC-chess, except for special promotion rules for a rook, bishop, and knight defined below.

If one of your knights on the board is self-captured, then the knight on the board is immediately promoted to a princess. The princess is demoted to a knight as soon as the self-captured knight is dropped onto the board. If both of your knights are self-captured, then one of them is dropped with a princess power and keeps it until the other knight is dropped. However, when one of your knights is captured by an enemy piece, the on-board knight is not promoted.

Accordingly, a knight on the board, the other on the airfield, then the on-board knight keeps promoted.

Suppose one of your knights is captured by your opponent, the other is on the board, and your opponent's two knights are on the board. If you capture one of your opponent's knights, then by the rule of SC-chess, you and your opponent's knights are exchanged and go to their airfields. Hence on-board knights are immediately promoted, not only yours but also your opponent's.

Promotion rules for a rook and a bishop are very similar.

Sample Problem

The following is a problem with Power mover for a promotion example. There are no pieces in the airfield or prison of white, and the rest pieces are all in the airfield or prison of black.

Black prison

All the rest white pieces

White airfield

None

Black airfield

All the rest black pieces

White prison

None

[Solution]: Pg8=Q+ Kxg8 Nxf6 Kh8 B+xe6 Q*g7 B+g8.

Just after Nxf6, the white bishop d7 is promoted to a queen (denoted by B+). By B+xe6, white captures a black knight, and so imprisoned black and white knights are exchanged immediately, that promotes the on-board black and white knights to princesses. Q*g7 means that a queen is dropped onto g7.

Notes

Promotion is usually performed by entering some special area, a pawn in ordinary chess, or especially in shogi, most pieces are promoted when they enter the opponent's area. But Power mover performs promotion in a different way (except pawn), that makes it possible to do with only the ordinary chess set.

The promotion rules themselves make a game more difficult and interesting, because the two states "one promoted piece" and "two unpromoted pieces" are well-balanced and an advantageous choice depends on the situation.