If you put the constraint that an 'x' set of connections on a square board is not allowed - ox x. So that 'o' is prohibited from playing in the empty spot

If you put the constraint that an 'x' set of connections on a square board is not allowed - ox x. So that 'o' is prohibited from playing in the empty spot there because 'x' already has a connection - you get the game Crossway - https://boardgamegeek.com/boardgame/30517/crossway https://boardgamegeek.com/boardgame/30517/crossway // http://superdupergames.org/gameinfo.html?game=cross http://superdupergames.org/gameinfo.html?game=cross // http://www.marksteeregames.com/Crossway_rules.pdf http://www.marksteeregames.com/Crossway_rules.pdf