1. The problem statement, all variables and given/known data Consider the game of `double move tic-tac-toe' played by the usual rules of tic- tac-toe, except that each player makes two marks in succession before relinquishing his turn to the other player (you may know tic-tac-toe by the name `noughts and crosses'). Prove that there exists a strategy by which the first player always wins. 2. Relevant equations None that I can think of. 3. The attempt at a solution I have no clue how to prove this. The obvious strategy is that player one places an X at one of the corners of the board and then one in the center. Player two can't block all the winning strategies with their two moves. The question is, how do I show this in "math speak"? Thanks! Sorry for all the posting lately, I'm just terrible at Discrete Math.