user86: If one player (Black) gives another player (White) odds of x moves, stipulating that White must not move any man beyond his fourth rank until Black has made one move, what's the smallest value for "x" that would force checkmate by the time it is Black's turn to move?  And what would those x moves be?

user2299: I think something like this is the easiest solution. The set-up takes 16 moves, but then it's only two more moves to checkmate and you don't need a computer to verify it. This is almost the same as Akavall's set-up, except that a knight is posted on c4 instead of g4.
[FEN ""]

1. a4 null 2. d4 null 3. h4 null 4. Nf3 null 5. Na3 null 6. Nd2 null 7. Ne4 null 8. Nc4 null 9. Qd2 null 10. Qf4 null 11. Ra3 null 12. Re3 null 13. Rhh3 null 14. Rhf3 null 15. g3 null 16. Bh3

But you can stop after only 14 moves, and Stockfish announces a forced mate in 7. (Note that after 14. Rhf3 White is threatening both 15. Qxf7# and 15. Nd6+ followed by 16. Nxd6#; only by moving the d pawn can Black parry both threats.)
[FEN ""]

1. a4 null 2. d4 null 3. h4 null 4. Nf3 null 5. Na3 null 6. Nd2 null 7. Ne4 null 8. Nc4 null 9. Qd2 null 10. Qf4 null 11. Ra3 null 12. Re3 null 13. Rhh3 null 14. Rhf3 d6 (14... d5 15. Qxf7+ Kd7 16. Ne5#) 15. Qxf7+ Kd7 16. Nc5+ dxc5 (16... Kc6 17. Na5+ Kb6 18. Qb3+ Kxa5 19. Qb5#) 17. Ne5+ Kd6 18. dxc5+ Kxc5 19. Qc4+ Kd6 (19... Kb6 20. Qb5#) 20. Qd4+ Ke6 21. Nd3#


user307: Interesting puzzle. 
I came up with this.
[FEN ""]

1. d4 null 2. Qd2 null 3. Qf4 null 4. a4 null 5. Ra3 null 6. Re3 null 7. Nf3 null 8. h4 null 9. Nh2 null 10. Ng4 null 11. Rhh3 null 12. Rhf3 null 13. Nc3 null 14. Ne4 null 15. g3

After Black makes any move, it is a forced checkmate according Houdini. The best move is ’15... f6.’ It allows for mate in 10 moves.

86: <p>If one player (Black) gives another player (White) odds of x moves, stipulating that White must not move any man beyond his fourth rank until Black has made one move, what's the smallest value for "x" that would force checkmate by the time it is Black's turn to move?  And what would those x moves be?</p>
 2299: <p>I think something like this is the easiest solution. The set-up takes <strong>16 moves,</strong> but then it's only two more moves to checkmate and you don't need a computer to verify it. This is almost the same as Akavall's set-up, except that a knight is posted on c4 instead of g4.</p>
<pre><code>[FEN &quot;&quot;]

1. a4 null 2. d4 null 3. h4 null 4. Nf3 null 5. Na3 null 6. Nd2 null 7. Ne4 null 8. Nc4 null 9. Qd2 null 10. Qf4 null 11. Ra3 null 12. Re3 null 13. Rhh3 null 14. Rhf3 null 15. g3 null 16. Bh3
</code></pre>
<p>But you can stop after <strong>only 14 moves,</strong> and Stockfish announces a forced mate in 7. (Note that after 14. Rhf3 White is threatening both 15. Qxf7# and 15. Nd6+ followed by 16. Nxd6#; only by moving the d pawn can Black parry both threats.)</p>
<pre><code>[FEN &quot;&quot;]

1. a4 null 2. d4 null 3. h4 null 4. Nf3 null 5. Na3 null 6. Nd2 null 7. Ne4 null 8. Nc4 null 9. Qd2 null 10. Qf4 null 11. Ra3 null 12. Re3 null 13. Rhh3 null 14. Rhf3 d6 (14... d5 15. Qxf7+ Kd7 16. Ne5#) 15. Qxf7+ Kd7 16. Nc5+ dxc5 (16... Kc6 17. Na5+ Kb6 18. Qb3+ Kxa5 19. Qb5#) 17. Ne5+ Kd6 18. dxc5+ Kxc5 19. Qc4+ Kd6 (19... Kb6 20. Qb5#) 20. Qd4+ Ke6 21. Nd3#
</code></pre>
 307: <p>Interesting puzzle. </p>

<p>I came up with this.</p>

<pre><code>[FEN ""]

1. d4 null 2. Qd2 null 3. Qf4 null 4. a4 null 5. Ra3 null 6. Re3 null 7. Nf3 null 8. h4 null 9. Nh2 null 10. Ng4 null 11. Rhh3 null 12. Rhf3 null 13. Nc3 null 14. Ne4 null 15. g3
</code></pre>

<p>After Black makes any move, it is a forced checkmate according Houdini. The best move is ’15... f6.’ It allows for mate in 10 moves.</p>
