The Protracted Game: A Wei’chi Interpretation of Maoist Revolutionary Strategy, 1969:
The board takes the form of (…) nineteen horizontal and nineteen vertical lines equidistantly placed. (…) Other grid sizes are also used, the most common being 8x8, 13x13, and 17x17. It has been claimed that the strategic combinations posible (sic.) on a 23x23 or larger board would be beyond the range of the human mind.
Not 9x9 but rather 8x8?