Frontiers

A chess variant with four armies advancing into the board from four directions, but with adjacent pairs of armies allied. Thus White has a so-called "round front" and a "square front", advancing north and west respectively, while Black has a "round front" and a "square front" advancing south and east. All four armies take turns to play, so each player on their turn first makes a move with one of their square-front pieces, then with one of their round-front pieces. The object of the game is to