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<ol class="chapter"><li class="chapter-item expanded affix "><a href="../index.html">halo2</a></li><li class="chapter-item expanded "><a href="../concepts.html"><strong aria-hidden="true">1.</strong> Concepts</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../concepts/proofs.html"><strong aria-hidden="true">1.1.</strong> Proof systems</a></li><li class="chapter-item expanded "><a href="../concepts/arithmetization.html" class="active"><strong aria-hidden="true">1.2.</strong> PLONKish Arithmetization</a></li><li class="chapter-item expanded "><a href="../concepts/chips.html"><strong aria-hidden="true">1.3.</strong> Chips</a></li><li class="chapter-item expanded "><a href="../concepts/gadgets.html"><strong aria-hidden="true">1.4.</strong> Gadgets</a></li></ol></li><li class="chapter-item expanded "><a href="../user.html"><strong aria-hidden="true">2.</strong> User Documentation</a></li><li><ol class="section"><li class="chapter-item expanded "><a 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argument</a></li><li class="chapter-item expanded "><a href="../design/proving-system/multipoint-opening.html"><strong aria-hidden="true">4.1.5.</strong> Multipoint opening argument</a></li><li class="chapter-item expanded "><a href="../design/proving-system/inner-product.html"><strong aria-hidden="true">4.1.6.</strong> Inner product argument</a></li><li class="chapter-item expanded "><a href="../design/proving-system/comparison.html"><strong aria-hidden="true">4.1.7.</strong> Comparison to other work</a></li></ol></li><li class="chapter-item expanded "><a href="../design/protocol.html"><strong aria-hidden="true">4.2.</strong> Protocol Description</a></li><li class="chapter-item expanded "><a href="../design/implementation.html"><strong aria-hidden="true">4.3.</strong> Implementation</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../design/implementation/proofs.html"><strong aria-hidden="true">4.3.1.</strong> Proofs</a></li><li class="chapter-item expanded 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<h1 id="plonkish-arithmetization"><a class="header" href="#plonkish-arithmetization">PLONKish Arithmetization</a></h1>
<p>The arithmetization used by Halo 2 comes from <a href="https://eprint.iacr.org/2019/953">PLONK</a>, or
more precisely its extension UltraPLONK that supports custom gates and lookup arguments. We'll
call it <a href="https://twitter.com/feministPLT/status/1413815927704014850"><em><strong>PLONKish</strong></em></a>.</p>
<p><em><strong>PLONKish circuits</strong></em> are defined in terms of a rectangular matrix of values. We refer to
<em><strong>rows</strong></em>, <em><strong>columns</strong></em>, and <em><strong>cells</strong></em> of this matrix with the conventional meanings.</p>
<p>A PLONKish circuit depends on a <em><strong>configuration</strong></em>:</p>
<ul>
<li>
<p>A finite field <span class="katex"><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.6889em;"></span><span class="mord mathbb">F</span></span></span></span>, where cell values (for a given statement and witness) will be
elements of <span class="katex"><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.6889em;"></span><span class="mord mathbb">F</span></span></span></span>.</p>
</li>
<li>
<p>The number of columns in the matrix, and a specification of each column as being
<em><strong>fixed</strong></em>, <em><strong>advice</strong></em>, or <em><strong>instance</strong></em>. Fixed columns are fixed by the circuit;
advice columns correspond to witness values; and instance columns are normally used for
public inputs (technically, they can be used for any elements shared between the prover
and verifier).</p>
</li>
<li>
<p>A subset of the columns that can participate in equality constraints.</p>
</li>
<li>
<p>A <em><strong>maximum constraint degree</strong></em>.</p>
</li>
<li>
<p>A sequence of <em><strong>polynomial constraints</strong></em>. These are multivariate polynomials over
<span class="katex"><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.6889em;"></span><span class="mord mathbb">F</span></span></span></span> that must evaluate to zero <em>for each row</em>. The variables in a polynomial
constraint may refer to a cell in a given column of the current row, or a given column of
another row relative to this one (with wrap-around, i.e. taken modulo <span class="katex"><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.4306em;"></span><span class="mord mathnormal">n</span></span></span></span>). The maximum
degree of each polynomial is given by the maximum constraint degree.</p>
</li>
<li>
<p>A sequence of <em><strong>lookup arguments</strong></em> defined over tuples of <em><strong>input expressions</strong></em>
(which are multivariate polynomials as above) and <em><strong>table columns</strong></em>.</p>
</li>
</ul>
<p>A PLONKish circuit also defines:</p>
<ul>
<li>
<p>The number of rows <span class="katex"><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.4306em;"></span><span class="mord mathnormal">n</span></span></span></span> in the matrix. <span class="katex"><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.4306em;"></span><span class="mord mathnormal">n</span></span></span></span> must correspond to the size of a multiplicative
subgroup of <span class="katex"><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.7713em;"></span><span class="mord"><span class="mord mathbb">F</span><span class="msupsub"><span class="vlist-t"><span class="vlist-r"><span class="vlist" style="height:0.7713em;"><span style="top:-3.063em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mbin mtight">×</span></span></span></span></span></span></span></span></span></span></span>; typically a power of two.</p>
</li>
<li>
<p>A sequence of <em><strong>equality constraints</strong></em>, which specify that two given cells must have equal
values.</p>
</li>
<li>
<p>The values of the fixed columns at each row.</p>
</li>
</ul>
<p>From a circuit description we can generate a <em><strong>proving key</strong></em> and a <em><strong>verification key</strong></em>,
which are needed for the operations of proving and verification for that circuit.</p>
<blockquote>
<p>Note that we specify the ordering of columns, polynomial constraints, lookup arguments, and
equality constraints, even though these do not affect the meaning of the circuit. This makes
it easier to define the generation of proving and verification keys as a deterministic
process.</p>
</blockquote>
<p>Typically, a configuration will define polynomial constraints that are switched off and on by
<em><strong>selectors</strong></em> defined in fixed columns. For example, a constraint <span class="katex"><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.6389em;vertical-align:-0.1944em;"></span><span class="mord"><span class="mord mathnormal" style="margin-right:0.03588em;">q</span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist" style="height:0.3117em;"><span style="top:-2.55em;margin-left:-0.0359em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mathnormal mtight">i</span></span></span></span><span class="vlist-s"></span></span><span class="vlist-r"><span class="vlist" style="height:0.15em;"><span></span></span></span></span></span></span><span class="mspace" style="margin-right:0.2222em;"></span><span class="mbin"></span><span class="mspace" style="margin-right:0.2222em;"></span></span><span class="base"><span class="strut" style="height:1em;vertical-align:-0.25em;"></span><span class="mord mathnormal">p</span><span class="mopen">(</span><span class="mord">...</span><span class="mclose">)</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">=</span><span class="mspace" style="margin-right:0.2778em;"></span></span><span class="base"><span class="strut" style="height:0.6444em;"></span><span class="mord">0</span></span></span></span> can
be switched off for a particular row <span class="katex"><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.6595em;"></span><span class="mord mathnormal">i</span></span></span></span> by setting <span class="katex"><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.625em;vertical-align:-0.1944em;"></span><span class="mord"><span class="mord mathnormal" style="margin-right:0.03588em;">q</span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist" style="height:0.3117em;"><span style="top:-2.55em;margin-left:-0.0359em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mathnormal mtight">i</span></span></span></span><span class="vlist-s"></span></span><span class="vlist-r"><span class="vlist" style="height:0.15em;"><span></span></span></span></span></span></span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">=</span><span class="mspace" style="margin-right:0.2778em;"></span></span><span class="base"><span class="strut" style="height:0.6444em;"></span><span class="mord">0</span></span></span></span>. In this case we sometimes refer
to a set of constraints controlled by a set of selector columns that are designed to be used
together, as a <em><strong>gate</strong></em>. Typically there will be a <em><strong>standard gate</strong></em> that supports generic
operations like field multiplication and division, and possibly also <em><strong>custom gates</strong></em> that
support more specialized operations.</p>
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