An abstract strategy game is a board game with perfect information, no chance, and (usually) two players. Many of the world's classic board games, including chess, go, and mancala, fit into this category. Play is sometimes said to resemble a series of puzzles the players pose to each other. A purist's definition of an abstract strategy game requires that it cannot have random elements or hidden information. In practice, however, many games are commonly classed as abstract strategy games which do not strictly meet these criteria.