user12958: I saw the following puzzle recently in a newspaper:

Black to play and win 
6rk/6qp/2Bp4/P1pP1p2/3bnP2/6BQ/7P/5R1K w - - 0 1


My proposed solution was
1. ...   Nf2+

and the lines I foresaw were
2. Bxf2  Bxf2
3. Rxf2  Qg1 mate

2. Bxf2  Bxf2
3. (something else)  Qg1+
4. Rxg1  Rxg1 mate

2. Rxf2  Bxf2
3. Bxf2  Qa1+ and interposing B or Q only delays the end

However, the given solution was

 1. ...   Bf2!
2. Rxf2  ...
 (If 2. Bxf2?  Nxf2+  3. Rxf2   Qg1 mate)
 2. ...   Nxf2+
3. Bxf2  Qa1+ and white resigns

I can see three possibilities:

I missed something
My solution is as good as the official one
They're actually equivalent under transposition

Which is the case?

user12629: They aren't quite equivalent because of the differences in the position if White declines or partially declines the sacrifice (for example, after Nf2+ Rxf2 Bxf2, White doesn't have to retake the bishop - but after Bf2 Rxf2 Nf2+ declining the knight instantly loses the queen.)  But both should win, even if Bf2 is slightly better.

user7297: They're not equivalent, but your solution is just as good. In fact, it's more easy to find because Nf2+ is a 'forcing' move.

12958: <p>I saw the following puzzle recently in a newspaper:</p>

<blockquote>
  <h2>Black to play and win </h2>

<pre><code>6rk/6qp/2Bp4/P1pP1p2/3bnP2/6BQ/7P/5R1K w - - 0 1
</code></pre>
</blockquote>

<p>My proposed solution was</p>

<pre><code>1. ...   Nf2+
</code></pre>

<p>and the lines I foresaw were</p>

<pre><code>2. Bxf2  Bxf2
3. Rxf2  Qg1 mate

2. Bxf2  Bxf2
3. (something else)  Qg1+
4. Rxg1  Rxg1 mate

2. Rxf2  Bxf2
3. Bxf2  Qa1+ and interposing B or Q only delays the end
</code></pre>

<p>However, the given solution was</p>

<blockquote class="spoiler">
  <p> <pre>1. ...   Bf2!
2. Rxf2  ...</pre>
 (If <code>2. Bxf2?  Nxf2+  3. Rxf2   Qg1 mate</code>)
 <pre>2. ...   Nxf2+
3. Bxf2  Qa1+ and white resigns</pre></p>
</blockquote>

<p>I can see three possibilities:</p>

<ol>
<li>I missed something</li>
<li>My solution is as good as the official one</li>
<li>They're actually equivalent under transposition</li>
</ol>

<p>Which is the case?</p>
 12629: <p>They aren't quite equivalent because of the differences in the position if White declines or partially declines the sacrifice (for example, after Nf2+ Rxf2 Bxf2, White doesn't have to retake the bishop - but after Bf2 Rxf2 Nf2+ declining the knight instantly loses the queen.)  But both should win, even if Bf2 is slightly better.</p>
 7297: <p>They're not <em>equivalent</em>, but your solution is just as good. In fact, it's more easy to find because Nf2+ is a 'forcing' move.</p>
