user16568: How can black mate in 4 moves?
[FEN "6k1/p5rp/3p1PR1/3Pp2Q/qBK1Pp2/5P2/2P5/r5R1 b - - 0 1"]
[Event "Black to mate in 4 moves"]


user11629: This does not seem too difficult.

 Due to the threats against the black king, black is basically forced to check at each move. Also, obviously you don't want to allow the white king to escape via c3 or d3 towards e2 or d2 where it would be relatively save. 

With this in mind, the solution comes almost naturally:

 1... Qxc2+ 2. Bc3 (2. Kb5 Qe2+ (or Qd3+) 3. Kc6 Ra6++ (or Qa6++)) Qe2+ 3. Kb4 (3. Kb3 Qa2+ 4. Kb4 Qa4++) a5+ 4. Kb3 Qa2++ One thing you need to check is that the more natural 1... Qxc2+ 2. Bc3 Ra4+ does not lead to mate in 4 (but only to mate in 5)


16568: <p>How can black mate in 4 moves?</p>

<pre><code>[FEN "6k1/p5rp/3p1PR1/3Pp2Q/qBK1Pp2/5P2/2P5/r5R1 b - - 0 1"]
[Event "Black to mate in 4 moves"]
</code></pre>
 11629: <p>This does not seem too difficult.</p>

<blockquote class="spoiler">
  <p> Due to the threats against the black king, black is basically forced to check at each move. Also, obviously you don't want to allow the white king to escape via c3 or d3 towards e2 or d2 where it would be relatively save. </p>
</blockquote>

<p>With this in mind, the solution comes almost naturally:</p>

<blockquote class="spoiler">
  <p> 1... Qxc2+ 2. Bc3 (2. Kb5 Qe2+ (or Qd3+) 3. Kc6 Ra6++ (or Qa6++)) Qe2+ 3. Kb4 (3. Kb3 Qa2+ 4. Kb4 Qa4++) a5+ 4. Kb3 Qa2++ One thing you need to check is that the more natural 1... Qxc2+ 2. Bc3 Ra4+ does not lead to mate in 4 (but only to mate in 5)</p>
</blockquote>
