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<h1>The International Obfuscated C Code Contest</h1>
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<h2>2019/adamovsky - Most functional interpreter</h2>
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<h3>Unlambda interpreter</h3>
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<a class="Right" href="https://github.com/ioccc-src/winner/blob/master/2019/adamovsky/prog.orig.c">Original C</a>
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<h2 id="author">Author:</h2>
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<ul>
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<li>Name: <a href="../../authors.html#Ondrej_Adamovsky">Ondřej Adamovský</a><br>
|
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Location: <a href="../../location.html#CZ">CZ</a> - <em>Czech Republic</em> (<em>Czechia</em>)</li>
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<h2 id="to-build">To build:</h2>
|
||
<pre><code> make</code></pre>
|
||
<h3 id="bugs-and-misfeatures">Bugs and (Mis)features:</h3>
|
||
<p>The current status of this entry is:</p>
|
||
<blockquote>
|
||
<p><strong>STATUS: INABIAF - please DO NOT fix</strong></p>
|
||
</blockquote>
|
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<p>For more detailed information see <a href="../../bugs.html#2019_adamovsky">2019/adamovsky in bugs.html</a>.</p>
|
||
<h2 id="to-use">To use:</h2>
|
||
<pre><code> ./prog file.unl</code></pre>
|
||
<h2 id="try">Try:</h2>
|
||
<pre><code> ./try.sh</code></pre>
|
||
<h2 id="judges-remarks">Judges’ remarks:</h2>
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||
<p>Even after pre-processing and indenting, the C code of this entry it
|
||
is about as understandable as the Unlambda code.</p>
|
||
<p>Pretending that we don’t know a bit of functional programming :) and lacking a
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better way to understand the entry but to fuzz it, we stumbled on a string of
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||
bytes which crashed it:</p>
|
||
<pre><code> ````.0`.0`.0`c.0``sssss</code></pre>
|
||
<p>Functional programming is not a panacea against core dumps, after all.</p>
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||
<p>This can be demonstrated by:</p>
|
||
<pre><code> ./prog crash.unl</code></pre>
|
||
<h2 id="authors-remarks">Author’s remarks:</h2>
|
||
<h3 id="a-highly-structured-state-state-machine">A highly structured state state machine</h3>
|
||
<h3 id="purpose">Purpose:</h3>
|
||
<p>The purpose of this program is to allow you to play Colossal Cave Adventure as
|
||
implemented by <a href="https://github.com/irori/advent-unlambda" title="Adventure">Kunihiko Sakamoto</a>. As that was written in <a href="http://www.madore.org/~david/programs/unlambda/" title="Unlambda programming language">Unlambda programming
|
||
language</a> designed by David Alexander Madore it has to be an Unlambda interpreter.</p>
|
||
<h3 id="aesthetics">Aesthetics:</h3>
|
||
<p>The program grew a bit too long so I had to use several macros to downsize it.
|
||
That unfortunately reduced my options for program layout. I decided to separate
|
||
it into two portions: the initial macro section where I had limited resources
|
||
which you should disregard its shape, unless you like it, and the rest, which is a
|
||
separator in the form of a single line followed by a section signifying the
|
||
function of the program, a block with removed shape of lambda character. Even
|
||
the official IOCCC size tool acknowledges this: When you call <code>./iocccsize -i <prog.c</code>, using the <a href="https://github.com/ioccc-src/winner/blob/master/2019/iocccsize.c">2019 version of
|
||
iocccsize.c</a>, iocccsize returns <strong>955</strong>,
|
||
which is the Unicode codepoint of the <strong>λ</strong> character.</p>
|
||
<p>It might be a surprise for you that according to the IOCCC size tool the program is
|
||
actually a <code>one-liner</code>. It certainly was for me. I like to think the tool is overwhelmed
|
||
by the sheer length of the dividing line and totally overlooks the rest of the program.</p>
|
||
<h3 id="usage">Usage:</h3>
|
||
<p>When built directly using</p>
|
||
<pre><code> make</code></pre>
|
||
<p>the program (<code>prog</code>) accepts a single parameter with the name of an Unlambda program. You can
|
||
download the <a href="https://github.com/irori/advent-unlambda" title="Adventure">Colossal Cave Adventure</a> (the <a href="https://github.com/ioccc-src/winner/blob/master/2019/adamovsky/advent.unl">advent.unl</a> file)
|
||
and run it like this:</p>
|
||
<pre><code> ./prog advent.unl</code></pre>
|
||
<p><strong>NOTE</strong>: the file was added to the entry so there is no need to download it.</p>
|
||
<p>You can also try other programs from the Web. Many example programs are in the official
|
||
<a href="http://www.madore.org/~david/programs/unlambda/#distrib" title="Reference Unlambda distribution">Unlambda distribution</a> on the Unlambda homepage. The most complex programs there are
|
||
entries from <a href="http://www.madore.org/~david/programs/unlambda/#quine" title="Unlambda quine contest">quine contest</a>.</p>
|
||
<p>There is an alternative build path that requires the 2018 IOCCC size tool to complete. Put the tool
|
||
source <a href="https://github.com/ioccc-src/winner/blob/master/2019/adamovsky/iocccsize_2018.c">iocccsize_2018.c</a> in the project directory and call</p>
|
||
<pre><code> make identify</code></pre>
|
||
<p>It will build the tool and use it to build an alternative program <code>prog2</code>, which in turn will
|
||
produce an Unlambda program <code>identify.unl</code>. <code>make identify</code> runs this program to identify
|
||
itself.</p>
|
||
<p>The base program (<code>prog</code>) implements an interpreter of Unlambda 2.0. It
|
||
recognises all its builtins (<code>k</code>, <code>s</code>, <code>i</code>, <code>v</code>, <code>c</code>, <code>d</code>, <code>.x</code>, <code>e</code>, <code>@</code>, <code>?x</code>
|
||
and <code>|</code>) including the syntactic sugar function <code>r</code> and formatting properties in
|
||
the form of ignoring whitespace and comments to the end of line introduced by
|
||
the <code>#</code> character.</p>
|
||
<p>In case of wrong usage (missing Unlambda program file or missing parameter) or
|
||
use of an unseekable (<code>fseek(3)</code>) Unlambda program source if it uses the <code>c</code>
|
||
function, the program returns the message <code>fail</code>. It also informs you about
|
||
syntactic errors in the Unlambda program should there be any (but only when the
|
||
execution reaches them).</p>
|
||
<p>The Unlambda source file may contain several Unlambda programs. The interpreter
|
||
will run them all in sequence.</p>
|
||
<h3 id="unlambda">Unlambda</h3>
|
||
<p>If you want to familiarise yourself with the language, visit its <a href="https://en.wikipedia.org/wiki/Unlambda" title="Unlambda on Wikipedia">Wikipedia page</a> for
|
||
a brief introduction or its <a href="http://www.madore.org/~david/programs/unlambda/" title="Unlambda programming language">homepage</a> for an in depth discussion. For further reading you
|
||
can visit Wikipedia pages on <a href="https://en.wikipedia.org/wiki/Lambda_calculus" title="Lambda Calculus on Wikipedia">Lambda Calculus</a> and <a href="https://en.wikipedia.org/wiki/Combinatory_logic" title="Combinatory Logic on Wikipedia">Combinatory Logic</a>.</p>
|
||
<p>You can also play with an <a href="https://inazz.jp/unlambda/" title="Online Unlambda interpreter">online interpreter</a> by GitHub user inazz. There you can
|
||
debug one of the example programs provided or try your wits in writing your own.</p>
|
||
<h3 id="hints">Hints:</h3>
|
||
<p>Here are some pointers where to start when trying to understand the interpreter:</p>
|
||
<ul>
|
||
<li>Where are syntax errors detected?</li>
|
||
<li>How is the memory managed?</li>
|
||
<li>How does a program character turn into a function?</li>
|
||
<li>How does exit function <code>e</code> work?</li>
|
||
<li>Can <code>fD0</code> function be called?</li>
|
||
<li>Are the function names familiar? (warning: some are misleading)</li>
|
||
</ul>
|
||
<h3 id="obfuscation-sources">Obfuscation sources</h3>
|
||
<ul>
|
||
<li>The elephant in the room is the Unlambda language. As we all know, functional
|
||
programming defies sanity. Furthermore, Unlambda was specifically designed to be
|
||
unintelligible and hard to code in. Most of its functions are quite simple and
|
||
straightforward to implement, but two make it a mess: the promise operator <code>d</code>
|
||
and the call with current continuation <code>c</code>.</li>
|
||
<li>Most of the additional obfuscation is derived from basic design choices. That
|
||
is, how the state of the program is stored and how the Unlambda functions are
|
||
implemented.</li>
|
||
</ul>
|
||
<p>More on this in the <a href="#obfuscation">Obfuscation</a> section.</p>
|
||
<h3 id="build-notes">Build notes:</h3>
|
||
<p>The program does not require any special treatment by compilers. Some warnings
|
||
had to be suppressed when compiling with <code>-Wall -Wextra -pedantic</code>. Those were
|
||
produced because of the formatting of the source code, not any programming
|
||
technique. Compilation with <code>clang -Weverything</code> produced many more warnings,
|
||
but those are only relevant for multi-source-file projects and some are really
|
||
questionable (e.g. <code>-Wdisabled-macro-expansion</code>).</p>
|
||
<h3 id="portability">Portability:</h3>
|
||
<p>Development was done on Debian 9 on x86-64 architecture using mainly Clang 3.8.1-24
|
||
and GCC 6.3.0. The source is C11 compliant and does not use any special properties
|
||
except the following:</p>
|
||
<ul>
|
||
<li>The interpreter sort of relies on tail call optimization. It works well even
|
||
without it, but the stack runs out quickly with some Unlambda programs (e.g.
|
||
<code>trivial.unl</code> example from the <a href="http://www.madore.org/~david/programs/unlambda/#distrib" title="Reference Unlambda distribution">reference Unlambda distribution</a> produces
|
||
segfault). Clang with <code>-O3</code> option does this optimization well and said example
|
||
does not segfault with it. I was not able to force GCC to optimize it out
|
||
(probably an operator fault).</li>
|
||
<li>The only data structure of the program (the <code>union</code>) had much more
|
||
members originally. I joined all integers to a single <code>long long</code> member in the
|
||
name of obfuscation. It is used for reference counting (only 1 for every
|
||
reference) among other uses. <code>size_t</code> should be used for that, but practically,
|
||
I think the memory would run out sooner than the reference counter in any real
|
||
world situation even when <code>size_t</code> is bigger than <code>long long</code>. It is also used
|
||
for storing <code>char</code>s for later printing. This might produce some warnings, but
|
||
since it was developed using <code>char</code>s it should be always used safely.</li>
|
||
</ul>
|
||
<h3 id="obfuscation">Obfuscation:</h3>
|
||
<ul>
|
||
<li><p>You can examine the <a href="https://github.com/ioccc-src/winner/blob/master/2019/adamovsky/deobfuscated.c">deobfuscated.c</a> file. It is the original
|
||
final version of the interpreter, before I started the downsizing. It accepts
|
||
one more optional parameter that specifies a filename for the output Unlambda
|
||
function (it’s the Unlambda function that remains after all function
|
||
applications are done). When no filename is provided, <code>stderr</code> is used.</p>
|
||
<p>The function <em>output</em> is used for this additional functionality. You can use
|
||
it while debugging to visualise current variables.</p></li>
|
||
<li><p>The Unlambda functions are represented by a record consisting of an array of
|
||
five multipurpose arguments. The first one refers to the function implementing
|
||
its application, the second and the third ones are for arguments of the
|
||
function, the fourth one is for stack building, and the fifth one is the
|
||
reference counter.</p>
|
||
<p>The function argument is used not only for evaluation of the functions, but also
|
||
as a state variable to decide whether we want to call it, or do something else.</p></li>
|
||
<li><p>The interpreter reads the Unlambda source as it interprets it, translating the
|
||
incoming character to a function using a constructor stored in translation array
|
||
<code>T</code>.</p>
|
||
<p>This means the interpreter must reposition in the source file whenever current
|
||
continuation is called.</p></li>
|
||
<li><p>The state of the interpreter is represented by trees representing evaluated
|
||
Unlambda functions stored on the C stack as local variables, plus the source
|
||
file position. When a current continuation is created, the stack is unwound
|
||
using the fourth argument of the nodes, stored in the continuation, and rebuilt
|
||
back resuming the evaluation. When its called, the stack is unwound and thrown
|
||
away, and the stack stored in the continuation is restored.</p>
|
||
<p>This makes implementation of a complete debugger a bit more challenging.</p>
|
||
<p>For this to work, the functions that do the work (i.e. make a series of applications
|
||
and/or evaluations each of which may be a call to current continuation), the <code>s</code>
|
||
combinator and the <code>`</code> application operation had to be broken down to pieces, one
|
||
for each application/evaluation and corresponding helper functions for stack
|
||
rebuilding. (the helper functions are named beginning with <code>r</code> instead of <code>f</code>)</p></li>
|
||
<li><p>The <code>`</code> application operation does the reading of the Unlambda source when
|
||
needed. It also implements the promise function. Whenever it would apply it, it
|
||
overwrites the Apply constructor in translation array <code>T</code>, changing its function
|
||
to build an unevaluated sub-tree that is later evaluated whenever the promise is
|
||
applied.</p></li>
|
||
<li><p>To further the obfuscation, I shortened the function names while downsizing,
|
||
but preserved their meaning (with the exception of Apply functions, which I
|
||
renamed to <code>Y</code> to possibly confuse with <code>Y</code> combinator). Simple functions retained
|
||
their names to misguide the reader to believe to know what is what. The names of
|
||
continuation and exit functions were swapped. The names of <code>S</code> and Apply functions
|
||
were shuffled both for <code>S</code> functions and Apply functions in the same way to hide
|
||
the meaning of <code>f</code> and <code>r</code> prefixes.</p></li>
|
||
</ul>
|
||
<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="identification">Identification</h3>
|
||
<p>The alternative build path <code>make identify</code> output commemorates a <a href="../../2014/birken/index.html" title="Best use of port 1701">previous IOCCC
|
||
winning entry</a> which uses similar methods to mess with the size tool.</p>
|
||
<h3 id="how-this-entry-works">How this entry works:</h3>
|
||
<p>It is not a bug, it is a feature. :)</p>
|
||
<p>The crash is caused by a stack overflow. Conventional Unlabmda interpreters
|
||
implement the Unlambda execution stack using data structures on the heap. This
|
||
interpreter uses the C call stack for this purpose. In a conventional
|
||
interpreter, the judges’ program would consume memory until the user (or the
|
||
operating system) would lose patience. The C call stack is usually of a limited
|
||
size and protected, so this interpreter crashes, when the judges’ program
|
||
depletes the stack. You can always increase the maximal stack size through the
|
||
system settings (on Linux) or compiler options (on Windows) if your Unlambda
|
||
program needs it. Nevertheless, it will not help the judges’ program which
|
||
quickly depletes any limit you define.</p>
|
||
<p>The judges, pretending to not know what they are doing, created a program that
|
||
grows Unlambda execution stack indefinitely. You may consider it an Unlambda
|
||
anti-pattern. Normally, infinite cycles in Unlambda work by creating two
|
||
functions and applying one to the other which creates further functions to
|
||
apply. The application of the function frees its position on the stack. This
|
||
program builds one ever growing function that will never be complete and be able to
|
||
be applied.</p>
|
||
<!--
|
||
|
||
Copyright © 1984-2024 by Landon Curt Noll. All Rights Reserved.
|
||
|
||
You are free to share and adapt this file under the terms of this license:
|
||
|
||
Creative Commons Attribution-ShareAlike 4.0 International (CC BY-SA 4.0)
|
||
|
||
For more information, see:
|
||
|
||
https://creativecommons.org/licenses/by-sa/4.0/
|
||
|
||
-->
|
||
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|
||
|
||
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|
||
|
||
<div id="inventory">
|
||
<h1 id="inventory-for-2019adamovsky">Inventory for 2019/adamovsky</h1>
|
||
</div>
|
||
<h2 id="primary-files">Primary files</h2>
|
||
<ul>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2019/adamovsky/prog.c">prog.c</a> - entry source code</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2019/adamovsky/Makefile">Makefile</a> - entry Makefile</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2019/adamovsky/prog.orig.c">prog.orig.c</a> - original source code</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2019/adamovsky/try.sh">try.sh</a> - script to try entry</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2019/adamovsky/advent.unl">advent.unl</a> - unlambda script</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2019/adamovsky/crash.unl">crash.unl</a> - unlambda script</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2019/adamovsky/deobfuscated.c">deobfuscated.c</a> - deobfuscated source code</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2019/adamovsky/iocccsize_2018.c">iocccsize_2018.c</a> - 2018 iocccsize.c source</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2019/adamovsky/sierpinski.unl">sierpinski.unl</a> - unlambda code</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2019/adamovsky/spam.unl">spam.unl</a> - unlambda code</li>
|
||
</ul>
|
||
<h2 id="secondary-files">Secondary files</h2>
|
||
<ul>
|
||
<li><a href="2019_adamovsky.tar.bz2">2019_adamovsky.tar.bz2</a> - download entry tarball</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2019/adamovsky/README.md">README.md</a> - markdown source for this web page</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2019/adamovsky/.entry.json">.entry.json</a> - entry summary and manifest in JSON</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2019/adamovsky/.gitignore">.gitignore</a> - list of files that should not be committed under git</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2019/adamovsky/.path">.path</a> - directory path from top level directory</li>
|
||
<li><a href="index.html">index.html</a> - this web page</li>
|
||
</ul>
|
||
<hr style="width:10%;text-align:left;margin-left:0">
|
||
<h4>
|
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Jump to: <a href="#">top</a>
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<!--
|
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|
||
Copyright © 1984-2025 by Landon Curt Noll. All Rights Reserved.
|
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|
||
You are free to share and adapt this file under the terms of this license:
|
||
|
||
Creative Commons Attribution-ShareAlike 4.0 International (CC BY-SA 4.0)
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|
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For more information, see:
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|
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https://creativecommons.org/licenses/by-sa/4.0/
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||
|
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-->
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<div class="footer">
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<div id="copyright"><h3>Copyright © 1984-2025 by Landon Curt Noll:
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<a href="https://creativecommons.org/faq/#what-does-some-rights-reserved-mean"
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||
target="_blank"
|
||
rel="license noopener noreferrer">Some Rights Reserved</a></h3>
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<p>
|
||
This work is <b>licensed by Landon Curt Noll</b> under
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<b><a href="https://creativecommons.org/licenses/by-sa/4.0/?ref=chooser-v1"
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target="_blank"
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rel="license noopener noreferrer"
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style="display:inline-block;">CC BY-SA 4.0</a></b>.
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src="../../png/cc.png"
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You should <b>carefully review</b> the
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rel="license noopener noreferrer">CC BY-SA 4.0 LEGAL CODE</a></b>
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before using the licensed material.<br>
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You may wish to review the
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<b><a href="../../license.html"
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rel="license noopener noreferrer">highlights of some of the key features and terms</a></b>
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of <b>CC BY-SA 4.0</b>.<br>
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</div>
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|
||
<div id="coda"><h3>Coda</h3>
|
||
<p>
|
||
<a href="https://validator.w3.org/nu/?doc=https%3A%2F%2Fwww.ioccc.org%2F2019%2Fadamovsky%2Findex.html" rel="nofollow">Nu HTML check this web page</a><br>
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