5. If not, could his adversary, if he had the move, win the game.
6. If so, Automaton must prevent him if possible.
7. If his adversary cannot win the game at his next move, Automaton must examine whether he can make such a move that, if he were allowed to have two moves in succession, he could at the second move have two different ways of winning the game;and each of these cases failing, Automaton must look forward to three or more successive moves.
Now I have already stated that in the Analytical Engine I had devised mechanical means equivalent to memory, also that I had provided other means equivalent to foresight, and that the Engine itself could act on this foresight.
In consequence of this the whole question of making an automaton play any game depended upon the possibility of the machine being able to represent all the myriads of combinations relating to it. Allowing one hundred moves on each side for the longest game at chess, I found that the combinations involved in the Analytical Engine enormously surpassed any required, even by the game of chess.
As soon as I had arrived at this conclusion I commenced an examination of a game called "tit-tat-to," usually played by little children. It is the simplest game with which I am acquainted. Each player has five counters, one set marked with a +, the other set with an O. The board consists of a square divided into nine smaller squares, and the object of each player is to get three of his own men in a straight
