Cờ Trận (Tactical Formation): Documenting and Analysing a Vietnamese Folk Board Game for 2–4 Players

Many Vietnamese folk board games survive only by word of mouth and are easily forgotten. Cờ Trận is one such game. It was played in Đồng Bùa hamlet, Tam Quan commune, Tam Đảo district, Vĩnh Phúc province, using whatever could be picked up by the roadside as pieces: stones, pebbles, twigs, leaves. To our knowledge it has never been written down. This paper records the rules of Cờ Trận for two, three and four players, from the recollection of the author, who played it throughout grades 5 to 9. The English name Tactical Formation was given by the author. A piece moves by jumping over an adjacent piece of any side, and the jumped-over piece stays on the board. After landing, if a line of enemy pieces lies between the moved piece and a friendly piece, the player chooses one such line and that whole line changes side. The board has two layers of positions, vertices and centres: a vertex piece moves in 8 directions and a centre piece in 4. We give a formal mathematical model of the two-player mode, in which the total number of pieces is an invariant: capture is a change of side, never a removal. We also implement the game as open-source software, with an AI based on Minimax search with Alpha-Beta pruning (the Paranoid variant for the multiplayer modes). Experiments measure the branching factor, game length and the bots' think time. In the two-player mode deeper search wins consistently, and in 100 games between two bots of equal depth the loser was always blockaded with pieces left; no game ended by losing all pieces. Through a written record, a formal model and software that anyone can play, the paper helps preserve a folk game that is fading away. The rules of Cờ Trận are a Vietnamese folk tradition recorded from the author's recollection; the author did not invent the game. A Vietnamese translation of the paper is kept in the source repository.