Ashby used variety to analyze the problem of regulation by considering a two-player game, where one player, formula_12, supplies disturbances which another player, formula_13, must regulate to ensure acceptable outcomes. formula_12 and formula_13 each have a set of available moves, which choose the outcome from a table with as many rows as formula_12 has moves and as many columns as formula_13 has moves. formula_13 is allowed full knowledge of formula_12's move, and must pick moves in response so that the outcome is acceptable.