“…This is called a P-position. Secondly, as shown in Figure 5, the first player puts "O" in the corner compartment (1,1) and the second player draws in the compartment (1,2). In this case, if the first player knows the strategy for this game for the N-position, he will put it in the compartment (3,3), and if the second player draws in the compartment (2,3), at this time, the first player only has one choice, that is, to put it in the compartment (3,2) or (1,2), which is the same.…”