This is a very simple although interesting variant. The two bishops and
Knights of each bands are numbered 1 or 2. At the begining of the game,
each player annotates in a paper which of the two enemy Bishops or Knights
is the player´s Secret Agent (only one enemy piece). In every moment of
the game, the player may, as a move, change the color of the Secret Agent
and move it in the same turn, and the enemy piece changes to friend piece
for the rest of the game. Try it!
