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Related to this question, where there the solution was unexpected for us.

Let $n,m$ be positive integers, $n \le m \le n^2/2$.

The board is $n \times n$ square grid.

Phase 1:

  • Two players, $A,B$ make $m$ moves, where at each move each of them color uncolored vertex of the grid red.

Phase 2:

  • $A,B$ take moves in turns.

  • A move is picking two red vertices and drawing a straight line between them.

  • If the line intersects another line or passes through a third red vertex, the game ends and the player who made the move loses the game. Two or more lines are allowed to end at the same vertex.

Is there winning strategy depending on $n,m$?

If the general solution is hard fix $m$, say let $m=\lfloor \frac{n^2}{4} \rfloor$

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  • $\begingroup$ why would there ever be no valid moves? $\endgroup$
    – Squala
    Commented Jan 24, 2022 at 17:53
  • $\begingroup$ @Squala You are right, draw is impossible, I edited. $\endgroup$
    – joro
    Commented Jan 24, 2022 at 19:03
  • $\begingroup$ It says a move is coloring a vertex (or more than one vertex?) red, and then it says a move is drawing a line (segment, presumably) between two red vertices. Which is it? $\endgroup$ Commented Jan 25, 2022 at 5:52
  • $\begingroup$ @GerryMyerson Thanks, you are right. I edited, trying to clarify about two types of moves. $\endgroup$
    – joro
    Commented Jan 25, 2022 at 7:13
  • $\begingroup$ In phase 1, do the players move simultaneously or alternately? $\endgroup$
    – Eilon
    Commented Jan 25, 2022 at 14:36

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