add notices to those who wish for a greater challenge

We add the following level-3 header to help people identify text
they may wish to skip if they wish for a greater challenge:

```
```

After that notice we add:

```
**If you want a greater challenge, don't read any further**:
just try to understand the program via the source.

If you get stuck, come back and read below for additional hints and information.
```

And sometimes follow with:

```
```

Or sometimes follow with:

```
```

Where the alt code impacts a "greater challenge", we add instead:

```
**If you want a greater challenge, don't read any further**:
just try to understand the program without looking at the Alternate code.

If you get stuck, come back and look at the Alternate code.
```

And where a given command impacts a "greater challenge", we add instead:

```
**If you want a greater challenge, don't read any further**:
just try to understand the program without running the command below.

If you get stuck, come back and run the following command:
```

Perform `make www` to perform the above and test under macOS.

2012/tromp/index.html

@@ -743,8 +743,6 @@ separate <a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2012/
 and from a hardcoded sizeof of 4 to 8.</p>
 <p>The program has been tested to work correctly on Linux/Solaris/MacOSX both in 32
 and 64 bits.</p>
-<h3 id="how-the-program-works">How the program works</h3>
-<p>See the file <a href="how.html">how.html</a>.</p>
 <h3 id="acknowledgements">Acknowledgements</h3>
 <p>Christopher Hendrie, Bertram Felgenhauer, Alex Stangl, Seong-hoon Kang,
 and <a href="../../authors.html#Yusuke_Endoh">Yusuke Endoh</a> have contributed ideas and
@@ -759,6 +757,12 @@ Cambridge Tracts in Theoretical Computer Science, Cambridge University Press, Oc
 A call-by-name lambda-calculus machine
 Higher Order Symbol. Comput. 20, 3 (September 2007), 199-207.
 <a href="http://www.pps.univ-paris-diderot.fr/~krivine/articles/lazymach.pdf" class="uri">http://www.pps.univ-paris-diderot.fr/~krivine/articles/lazymach.pdf</a></p>
+<h3 id="notice-to-those-who-wish-for-a-greater-challenge">NOTICE to those who wish for a greater challenge</h3>
+<p><strong>If you want a greater challenge, don’t read any further</strong>:
+just try to understand the program via the source.</p>
+<p>If you get stuck, come back and read below for additional hints and information.</p>
+<h3 id="how-this-entry-works">How this entry works:</h3>
+<p>See the file <a href="how.html">how.html</a>.</p>
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