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<h1 id="firstHeading" class="firstHeading mw-first-heading"><span class="mw-page-title-main">Robinson-Arithmetik</span></h1>
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<div id="mw-content-text" class="mw-body-content mw-content-ltr" lang="de" dir="ltr"><div class="mw-content-ltr mw-parser-output" lang="de" dir="ltr"><p>Die <b>Robinson-Arithmetik</b> (auch: <b>Q</b>) ist ein endlich axiomatisiertes Fragment der <a href="Peano-Arithmetik" title="Peano-Arithmetik">Peano-Arithmetik</a>, eines <a href="Axiomensystem" title="Axiomensystem">Axiomensystems</a> der <a href="Arithmetik" title="Arithmetik">Arithmetik</a>, also der <a href="Nat%C3%BCrliche_Zahl" title="Natürliche Zahl">natürlichen Zahlen</a>, innerhalb der <a href="Pr%C3%A4dikatenlogik" title="Prädikatenlogik">Prädikatenlogik erster Stufe</a>. Sie wurde 1950 von <a href="Raphael_Robinson" title="Raphael Robinson">Raphael Robinson</a> eingeführt und entspricht im Wesentlichen der Peano-Arithmetik ohne das <a href="Axiomenschema" title="Axiomenschema">Axiomenschema</a> der <a href="Vollst%C3%A4ndige_Induktion" title="Vollständige Induktion">Induktion</a>. Die Bedeutung der Robinson-Arithmetik rührt daher, dass sie endlich axiomatisierbar, aber nicht rekursiv vervollständigbar ist und sogar <a href="Unentscheidbar" class="mw-redirect" title="Unentscheidbar">wesentlich unentscheidbar</a> ist. Dies bedeutet, dass es keine <a href="Widerspruchsfreiheit" title="Widerspruchsfreiheit">konsistente</a> entscheidbare Erweiterung der Robinson-Arithmetik gibt. Es gibt damit insbesondere auch keine <a href="Vollst%C3%A4ndigkeit_(Logik)" title="Vollständigkeit (Logik)">vollständige</a> <a href="Rekursiv_aufz%C3%A4hlbar" class="mw-redirect" title="Rekursiv aufzählbar">rekursiv aufzählbare</a> Erweiterung, da diese bereits rekursiv (entscheidbar) wäre.<sup id="cite_ref-1" class="reference"><a href="#cite_note-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup>
</p>
<div class="mw-heading mw-heading2"><h2 id="Axiome">Axiome</h2></div>
<p>Die Robinson-Arithmetik ist formuliert in der <a href="Pr%C3%A4dikatenlogik" title="Prädikatenlogik">Prädikatenlogik erster Stufe</a> mit <a href="Gleichheit" title="Gleichheit">Gleichheit</a>, repräsentiert durch das Prädikat <span class="mwe-math-element mwe-math-element-inline"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle =}">
<semantics>
<mrow class="MJX-TeXAtom-ORD">
<mstyle displaystyle="true" scriptlevel="0">
<mo>=</mo>
</mstyle>
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<annotation encoding="application/x-tex">{\displaystyle =}</annotation>
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</math></span><img src="./_assets_/eb734a37dd21ce173a46342d1cc64c92/505a4ceef454c69dffd23792c84b90f488543743.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: 0.307ex; margin-bottom: -0.478ex; width:1.808ex; height:1.343ex;" alt="{\displaystyle =}" loading="lazy"></span>. Ihre Sprache hat die Konstante <span class="mwe-math-element mwe-math-element-inline"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \mathbf {0} }">
<semantics>
<mrow class="MJX-TeXAtom-ORD">
<mstyle displaystyle="true" scriptlevel="0">
<mrow class="MJX-TeXAtom-ORD">
<mn mathvariant="bold">0</mn>
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</mstyle>
</mrow>
<annotation encoding="application/x-tex">{\displaystyle \mathbf {0} }</annotation>
</semantics>
</math></span><img src="./_assets_/eb734a37dd21ce173a46342d1cc64c92/62e8c650763635a93ddc69768c3c0c100afe985d.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.338ex; width:1.337ex; height:2.176ex;" alt="{\displaystyle \mathbf {0} }" loading="lazy"></span> (genannt Null), die Nachfolgerfunktion <span class="mwe-math-element mwe-math-element-inline"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle S}">
<semantics>
<mrow class="MJX-TeXAtom-ORD">
<mstyle displaystyle="true" scriptlevel="0">
<mi>S</mi>
</mstyle>
</mrow>
<annotation encoding="application/x-tex">{\displaystyle S}</annotation>
</semantics>
</math></span><img src="./_assets_/eb734a37dd21ce173a46342d1cc64c92/4611d85173cd3b508e67077d4a1252c9c05abca2.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.338ex; width:1.499ex; height:2.176ex;" alt="{\displaystyle S}" loading="lazy"></span> (für <i>successor</i>: Nachfolger), welche intuitiv zu einer gegebenen Zahl 1 addiert, sowie die Funktionen <span class="mwe-math-element mwe-math-element-inline"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle +}">
<semantics>
<mrow class="MJX-TeXAtom-ORD">
<mstyle displaystyle="true" scriptlevel="0">
<mo>+</mo>
</mstyle>
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<annotation encoding="application/x-tex">{\displaystyle +}</annotation>
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</math></span><img src="./_assets_/eb734a37dd21ce173a46342d1cc64c92/fe6ef363cd19902d1a7a71fb1c8b21e8ede52406.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.505ex; width:1.808ex; height:2.176ex;" alt="{\displaystyle +}" loading="lazy"></span> für Addition und <span class="mwe-math-element mwe-math-element-inline"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \times }">
<semantics>
<mrow class="MJX-TeXAtom-ORD">
<mstyle displaystyle="true" scriptlevel="0">
<mo>×<!-- × --></mo>
</mstyle>
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<annotation encoding="application/x-tex">{\displaystyle \times }</annotation>
</semantics>
</math></span><img src="./_assets_/eb734a37dd21ce173a46342d1cc64c92/0ffafff1ad26cbe49045f19a67ce532116a32703.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: 0.019ex; margin-bottom: -0.19ex; width:1.808ex; height:1.509ex;" alt="{\displaystyle \times }" loading="lazy"></span> für Multiplikation. Sie hat folgende Axiome, die elementare Eigenschaften der natürlichen Zahlen und der arithmetischen Operationen formalisieren:<sup id="cite_ref-2" class="reference"><a href="#cite_note-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup>
</p>
<ul><li>Null hat keinen Vorgänger: <span class="mwe-math-element mwe-math-element-inline"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle Sx\not =\mathbf {0} }">
<semantics>
<mrow class="MJX-TeXAtom-ORD">
<mstyle displaystyle="true" scriptlevel="0">
<mi>S</mi>
<mi>x</mi>
<mo>≠</mo>
<mrow class="MJX-TeXAtom-ORD">
<mn mathvariant="bold">0</mn>
</mrow>
</mstyle>
</mrow>
<annotation encoding="application/x-tex">{\displaystyle Sx\not =\mathbf {0} }</annotation>
</semantics>
</math></span><img src="./_assets_/eb734a37dd21ce173a46342d1cc64c92/a44b4ca1e4c68bb6f78ab6f66be817a0a746c6ed.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:7.264ex; height:2.676ex;" alt="{\displaystyle Sx\not =\mathbf {0} }" loading="lazy"></span></li>
<li>Verschiedene Zahlen haben verschiedene Nachfolger: <span class="mwe-math-element mwe-math-element-inline"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle (Sx=Sy)\rightarrow x=y}">
<semantics>
<mrow class="MJX-TeXAtom-ORD">
<mstyle displaystyle="true" scriptlevel="0">
<mo stretchy="false">(</mo>
<mi>S</mi>
<mi>x</mi>
<mo>=</mo>
<mi>S</mi>
<mi>y</mi>
<mo stretchy="false">)</mo>
<mo stretchy="false">→<!-- → --></mo>
<mi>x</mi>
<mo>=</mo>
<mi>y</mi>
</mstyle>
</mrow>
<annotation encoding="application/x-tex">{\displaystyle (Sx=Sy)\rightarrow x=y}</annotation>
</semantics>
</math></span><img src="./_assets_/eb734a37dd21ce173a46342d1cc64c92/6d84181eb989369c557cd18fb93a8fc17b1ec839.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:19.589ex; height:2.843ex;" alt="{\displaystyle (Sx=Sy)\rightarrow x=y}" loading="lazy"></span></li>
<li>Jede Zahl ist gleich Null oder hat einen Vorgänger: <span class="mwe-math-element mwe-math-element-inline"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle y=\mathbf {0} \vee \exists x(Sx=y)}">
<semantics>
<mrow class="MJX-TeXAtom-ORD">
<mstyle displaystyle="true" scriptlevel="0">
<mi>y</mi>
<mo>=</mo>
<mrow class="MJX-TeXAtom-ORD">
<mn mathvariant="bold">0</mn>
</mrow>
<mo>∨<!-- ∨ --></mo>
<mi mathvariant="normal">∃<!-- ∃ --></mi>
<mi>x</mi>
<mo stretchy="false">(</mo>
<mi>S</mi>
<mi>x</mi>
<mo>=</mo>
<mi>y</mi>
<mo stretchy="false">)</mo>
</mstyle>
</mrow>
<annotation encoding="application/x-tex">{\displaystyle y=\mathbf {0} \vee \exists x(Sx=y)}</annotation>
</semantics>
</math></span><img src="./_assets_/eb734a37dd21ce173a46342d1cc64c92/8353ee49d47d9aee46dd9551c2ed25305041ee83.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:19.688ex; height:2.843ex;" alt="{\displaystyle y=\mathbf {0} \vee \exists x(Sx=y)}" loading="lazy"></span></li>
<li>Rekursive Definition von Addition und Multiplikation:
<ul><li><span class="mwe-math-element mwe-math-element-inline"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle x+\mathbf {0} =x}">
<semantics>
<mrow class="MJX-TeXAtom-ORD">
<mstyle displaystyle="true" scriptlevel="0">
<mi>x</mi>
<mo>+</mo>
<mrow class="MJX-TeXAtom-ORD">
<mn mathvariant="bold">0</mn>
</mrow>
<mo>=</mo>
<mi>x</mi>
</mstyle>
</mrow>
<annotation encoding="application/x-tex">{\displaystyle x+\mathbf {0} =x}</annotation>
</semantics>
</math></span><img src="./_assets_/eb734a37dd21ce173a46342d1cc64c92/dca0e81ceb9483eb5d6b22e8fda682bbbbcb8d26.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.505ex; width:9.935ex; height:2.343ex;" alt="{\displaystyle x+\mathbf {0} =x}" loading="lazy"></span></li>
<li><span class="mwe-math-element mwe-math-element-inline"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle x+Sy=S(x+y)}">
<semantics>
<mrow class="MJX-TeXAtom-ORD">
<mstyle displaystyle="true" scriptlevel="0">
<mi>x</mi>
<mo>+</mo>
<mi>S</mi>
<mi>y</mi>
<mo>=</mo>
<mi>S</mi>
<mo stretchy="false">(</mo>
<mi>x</mi>
<mo>+</mo>
<mi>y</mi>
<mo stretchy="false">)</mo>
</mstyle>
</mrow>
<annotation encoding="application/x-tex">{\displaystyle x+Sy=S(x+y)}</annotation>
</semantics>
</math></span><img src="./_assets_/eb734a37dd21ce173a46342d1cc64c92/17a64af6a8746ef89e0a487d69d271e787d3aafc.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:18.557ex; height:2.843ex;" alt="{\displaystyle x+Sy=S(x+y)}" loading="lazy"></span></li>
<li><span class="mwe-math-element mwe-math-element-inline"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle x\times \mathbf {0} =\mathbf {0} }">
<semantics>
<mrow class="MJX-TeXAtom-ORD">
<mstyle displaystyle="true" scriptlevel="0">
<mi>x</mi>
<mo>×<!-- × --></mo>
<mrow class="MJX-TeXAtom-ORD">
<mn mathvariant="bold">0</mn>
</mrow>
<mo>=</mo>
<mrow class="MJX-TeXAtom-ORD">
<mn mathvariant="bold">0</mn>
</mrow>
</mstyle>
</mrow>
<annotation encoding="application/x-tex">{\displaystyle x\times \mathbf {0} =\mathbf {0} }</annotation>
</semantics>
</math></span><img src="./_assets_/eb734a37dd21ce173a46342d1cc64c92/07383e09af08f8befd5fc79719caf258184d5828.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.338ex; width:9.942ex; height:2.176ex;" alt="{\displaystyle x\times \mathbf {0} =\mathbf {0} }" loading="lazy"></span></li>
<li><span class="mwe-math-element mwe-math-element-inline"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle x\times Sy=(x\times y)+x}">
<semantics>
<mrow class="MJX-TeXAtom-ORD">
<mstyle displaystyle="true" scriptlevel="0">
<mi>x</mi>
<mo>×<!-- × --></mo>
<mi>S</mi>
<mi>y</mi>
<mo>=</mo>
<mo stretchy="false">(</mo>
<mi>x</mi>
<mo>×<!-- × --></mo>
<mi>y</mi>
<mo stretchy="false">)</mo>
<mo>+</mo>
<mi>x</mi>
</mstyle>
</mrow>
<annotation encoding="application/x-tex">{\displaystyle x\times Sy=(x\times y)+x}</annotation>
</semantics>
</math></span><img src="./_assets_/eb734a37dd21ce173a46342d1cc64c92/0407ac9dfc23567968c69451ebace550695382de.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:21.228ex; height:2.843ex;" alt="{\displaystyle x\times Sy=(x\times y)+x}" loading="lazy"></span></li></ul></li></ul>
<div class="mw-heading mw-heading2"><h2 id="Bedeutsamkeit_für_die_Mathematische_Logik"><span id="Bedeutsamkeit_f.C3.BCr_die_Mathematische_Logik"></span>Bedeutsamkeit für die Mathematische Logik</h2></div>
<p>Die Robinson-Arithmetik spielt insbesondere beim <a href="Beweise_der_g%C3%B6delschen_Unvollst%C3%A4ndigkeitss%C3%A4tze" title="Beweise der gödelschen Unvollständigkeitssätze">Beweis des ersten Gödelschen Unvollständigkeitssatzes</a> eine Rolle,
da sich innerhalb von <b>Q</b> und ebenso in <a href="Widerspruchsfreiheit" title="Widerspruchsfreiheit">konsistenten</a> axiomatischen Erweiterungen von <b>Q</b> die Beziehung „… ist ein Beweis der Formel …“ repräsentieren lässt.<sup id="cite_ref-3" class="reference"><a href="#cite_note-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup>
</p><p>Dabei bedeutet Repräsentierbarkeit eines Prädikats <span class="mwe-math-element mwe-math-element-inline"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle P}">
<semantics>
<mrow class="MJX-TeXAtom-ORD">
<mstyle displaystyle="true" scriptlevel="0">
<mi>P</mi>
</mstyle>
</mrow>
<annotation encoding="application/x-tex">{\displaystyle P}</annotation>
</semantics>
</math></span><img src="./_assets_/eb734a37dd21ce173a46342d1cc64c92/b4dc73bf40314945ff376bd363916a738548d40a.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.338ex; width:1.745ex; height:2.176ex;" alt="{\displaystyle P}" loading="lazy"></span>, dass es eine Formel <span class="mwe-math-element mwe-math-element-inline"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \alpha =\alpha (x_{1},\ldots ,x_{n})}">
<semantics>
<mrow class="MJX-TeXAtom-ORD">
<mstyle displaystyle="true" scriptlevel="0">
<mi>α<!-- α --></mi>
<mo>=</mo>
<mi>α<!-- α --></mi>
<mo stretchy="false">(</mo>
<msub>
<mi>x</mi>
<mrow class="MJX-TeXAtom-ORD">
<mn>1</mn>
</mrow>
</msub>
<mo>,</mo>
<mo>…<!-- … --></mo>
<mo>,</mo>
<msub>
<mi>x</mi>
<mrow class="MJX-TeXAtom-ORD">
<mi>n</mi>
</mrow>
</msub>
<mo stretchy="false">)</mo>
</mstyle>
</mrow>
<annotation encoding="application/x-tex">{\displaystyle \alpha =\alpha (x_{1},\ldots ,x_{n})}</annotation>
</semantics>
</math></span><img src="./_assets_/eb734a37dd21ce173a46342d1cc64c92/8661d8520b6d0ec3f5ce1b9ab1b3cca4655f0e9d.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:17.993ex; height:2.843ex;" alt="{\displaystyle \alpha =\alpha (x_{1},\ldots ,x_{n})}" loading="lazy"></span> gibt,
so dass für alle natürlichen Zahlen <span class="mwe-math-element mwe-math-element-inline"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle a_{1},\ldots ,a_{n}}">
<semantics>
<mrow class="MJX-TeXAtom-ORD">
<mstyle displaystyle="true" scriptlevel="0">
<msub>
<mi>a</mi>
<mrow class="MJX-TeXAtom-ORD">
<mn>1</mn>
</mrow>
</msub>
<mo>,</mo>
<mo>…<!-- … --></mo>
<mo>,</mo>
<msub>
<mi>a</mi>
<mrow class="MJX-TeXAtom-ORD">
<mi>n</mi>
</mrow>
</msub>
</mstyle>
</mrow>
<annotation encoding="application/x-tex">{\displaystyle a_{1},\ldots ,a_{n}}</annotation>
</semantics>
</math></span><img src="./_assets_/eb734a37dd21ce173a46342d1cc64c92/451345cc97e2ed923dd4656fcc400c3f37119cca.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.671ex; width:9.911ex; height:2.009ex;" alt="{\displaystyle a_{1},\ldots ,a_{n}}" loading="lazy"></span> gilt:
</p>
<dl><dd>(+) falls <span class="mwe-math-element mwe-math-element-inline"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle P(a_{1},\ldots ,a_{n})}">
<semantics>
<mrow class="MJX-TeXAtom-ORD">
<mstyle displaystyle="true" scriptlevel="0">
<mi>P</mi>
<mo stretchy="false">(</mo>
<msub>
<mi>a</mi>
<mrow class="MJX-TeXAtom-ORD">
<mn>1</mn>
</mrow>
</msub>
<mo>,</mo>
<mo>…<!-- … --></mo>
<mo>,</mo>
<msub>
<mi>a</mi>
<mrow class="MJX-TeXAtom-ORD">
<mi>n</mi>
</mrow>
</msub>
<mo stretchy="false">)</mo>
</mstyle>
</mrow>
<annotation encoding="application/x-tex">{\displaystyle P(a_{1},\ldots ,a_{n})}</annotation>
</semantics>
</math></span><img src="./_assets_/eb734a37dd21ce173a46342d1cc64c92/27b895f6f6db52d2580053768a7ffea2ca3e9d71.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:13.465ex; height:2.843ex;" alt="{\displaystyle P(a_{1},\ldots ,a_{n})}" loading="lazy"></span> der Fall ist, dann ist die Aussage <span class="mwe-math-element mwe-math-element-inline"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \alpha ({\underline {a_{1}}},\ldots ,{\underline {a_{n}}})}">
<semantics>
<mrow class="MJX-TeXAtom-ORD">
<mstyle displaystyle="true" scriptlevel="0">
<mi>α<!-- α --></mi>
<mo stretchy="false">(</mo>
<mrow class="MJX-TeXAtom-ORD">
<munder>
<msub>
<mi>a</mi>
<mrow class="MJX-TeXAtom-ORD">
<mn>1</mn>
</mrow>
</msub>
<mo>_<!-- _ --></mo>
</munder>
</mrow>
<mo>,</mo>
<mo>…<!-- … --></mo>
<mo>,</mo>
<mrow class="MJX-TeXAtom-ORD">
<munder>
<msub>
<mi>a</mi>
<mrow class="MJX-TeXAtom-ORD">
<mi>n</mi>
</mrow>
</msub>
<mo>_<!-- _ --></mo>
</munder>
</mrow>
<mo stretchy="false">)</mo>
</mstyle>
</mrow>
<annotation encoding="application/x-tex">{\displaystyle \alpha ({\underline {a_{1}}},\ldots ,{\underline {a_{n}}})}</annotation>
</semantics>
</math></span><img src="./_assets_/eb734a37dd21ce173a46342d1cc64c92/5d294fba85702852dc9a99c99c108160da01ec86.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.877ex; margin-bottom: -0.795ex; width:13.212ex; height:3.676ex;" alt="{\displaystyle \alpha ({\underline {a_{1}}},\ldots ,{\underline {a_{n}}})}" loading="lazy"></span> in <b>Q</b> beweisbar,</dd>
<dd>(-) falls <span class="mwe-math-element mwe-math-element-inline"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle P(a_{1},\ldots ,a_{n})}">
<semantics>
<mrow class="MJX-TeXAtom-ORD">
<mstyle displaystyle="true" scriptlevel="0">
<mi>P</mi>
<mo stretchy="false">(</mo>
<msub>
<mi>a</mi>
<mrow class="MJX-TeXAtom-ORD">
<mn>1</mn>
</mrow>
</msub>
<mo>,</mo>
<mo>…<!-- … --></mo>
<mo>,</mo>
<msub>
<mi>a</mi>
<mrow class="MJX-TeXAtom-ORD">
<mi>n</mi>
</mrow>
</msub>
<mo stretchy="false">)</mo>
</mstyle>
</mrow>
<annotation encoding="application/x-tex">{\displaystyle P(a_{1},\ldots ,a_{n})}</annotation>
</semantics>
</math></span><img src="./_assets_/eb734a37dd21ce173a46342d1cc64c92/27b895f6f6db52d2580053768a7ffea2ca3e9d71.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:13.465ex; height:2.843ex;" alt="{\displaystyle P(a_{1},\ldots ,a_{n})}" loading="lazy"></span> nicht zutrifft, dann ist die Aussage <span class="mwe-math-element mwe-math-element-inline"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \neg \alpha ({\underline {a_{1}}},\ldots ,{\underline {a_{n}}})}">
<semantics>
<mrow class="MJX-TeXAtom-ORD">
<mstyle displaystyle="true" scriptlevel="0">
<mi mathvariant="normal">¬<!-- ¬ --></mi>
<mi>α<!-- α --></mi>
<mo stretchy="false">(</mo>
<mrow class="MJX-TeXAtom-ORD">
<munder>
<msub>
<mi>a</mi>
<mrow class="MJX-TeXAtom-ORD">
<mn>1</mn>
</mrow>
</msub>
<mo>_<!-- _ --></mo>
</munder>
</mrow>
<mo>,</mo>
<mo>…<!-- … --></mo>
<mo>,</mo>
<mrow class="MJX-TeXAtom-ORD">
<munder>
<msub>
<mi>a</mi>
<mrow class="MJX-TeXAtom-ORD">
<mi>n</mi>
</mrow>
</msub>
<mo>_<!-- _ --></mo>
</munder>
</mrow>
<mo stretchy="false">)</mo>
</mstyle>
</mrow>
<annotation encoding="application/x-tex">{\displaystyle \neg \alpha ({\underline {a_{1}}},\ldots ,{\underline {a_{n}}})}</annotation>
</semantics>
</math></span><img src="./_assets_/eb734a37dd21ce173a46342d1cc64c92/8d3e1a98a225df4a72ced2d14669fac0847f513a.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.877ex; margin-bottom: -0.795ex; width:14.762ex; height:3.676ex;" alt="{\displaystyle \neg \alpha ({\underline {a_{1}}},\ldots ,{\underline {a_{n}}})}" loading="lazy"></span> in <b>Q</b> beweisbar.<sup id="cite_ref-4" class="reference"><a href="#cite_note-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup></dd></dl>
<p>Der Term <span class="mwe-math-element mwe-math-element-inline"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {\underline {a}}}">
<semantics>
<mrow class="MJX-TeXAtom-ORD">
<mstyle displaystyle="true" scriptlevel="0">
<mrow class="MJX-TeXAtom-ORD">
<munder>
<mi>a</mi>
<mo>_<!-- _ --></mo>
</munder>
</mrow>
</mstyle>
</mrow>
<annotation encoding="application/x-tex">{\displaystyle {\underline {a}}}</annotation>
</semantics>
</math></span><img src="./_assets_/eb734a37dd21ce173a46342d1cc64c92/d1445f492dd189617565276b0d8eab56e463244e.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.534ex; margin-bottom: -0.804ex; width:1.232ex; height:2.676ex;" alt="{\displaystyle {\underline {a}}}" loading="lazy"></span> ist dabei wie folgt definiert:
</p>
<dl><dd><span class="mwe-math-element mwe-math-element-inline"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {\underline {0}}=\mathbf {0} }">
<semantics>
<mrow class="MJX-TeXAtom-ORD">
<mstyle displaystyle="true" scriptlevel="0">
<mrow class="MJX-TeXAtom-ORD">
<munder>
<mn>0</mn>
<mo>_<!-- _ --></mo>
</munder>
</mrow>
<mo>=</mo>
<mrow class="MJX-TeXAtom-ORD">
<mn mathvariant="bold">0</mn>
</mrow>
</mstyle>
</mrow>
<annotation encoding="application/x-tex">{\displaystyle {\underline {0}}=\mathbf {0} }</annotation>
</semantics>
</math></span><img src="./_assets_/eb734a37dd21ce173a46342d1cc64c92/0f6d0f163f8a14d82fb1626ef359bc3113305e80.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.562ex; margin-bottom: -0.776ex; width:5.598ex; height:3.176ex;" alt="{\displaystyle {\underline {0}}=\mathbf {0} }" loading="lazy"></span>,</dd>
<dd><span class="mwe-math-element mwe-math-element-inline"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {\underline {n+1}}=S{\underline {n}}}">
<semantics>
<mrow class="MJX-TeXAtom-ORD">
<mstyle displaystyle="true" scriptlevel="0">
<mrow class="MJX-TeXAtom-ORD">
<munder>
<mrow>
<mi>n</mi>
<mo>+</mo>
<mn>1</mn>
</mrow>
<mo>_<!-- _ --></mo>
</munder>
</mrow>
<mo>=</mo>
<mi>S</mi>
<mrow class="MJX-TeXAtom-ORD">
<munder>
<mi>n</mi>
<mo>_<!-- _ --></mo>
</munder>
</mrow>
</mstyle>
</mrow>
<annotation encoding="application/x-tex">{\displaystyle {\underline {n+1}}=S{\underline {n}}}</annotation>
</semantics>
</math></span><img src="./_assets_/eb734a37dd21ce173a46342d1cc64c92/0f3b23af5c53b60813fec4eddbbfca4396be8fca.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.701ex; margin-bottom: -0.803ex; width:11.395ex; height:3.343ex;" alt="{\displaystyle {\underline {n+1}}=S{\underline {n}}}" loading="lazy"></span>.<sup id="cite_ref-5" class="reference"><a href="#cite_note-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup></dd></dl>
<p>Das zugehörige Beweisbarkeitsprädikat „… ist beweisbar“ (d. h. „es gibt ein <span class="mwe-math-element mwe-math-element-inline"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle b}">
<semantics>
<mrow class="MJX-TeXAtom-ORD">
<mstyle displaystyle="true" scriptlevel="0">
<mi>b</mi>
</mstyle>
</mrow>
<annotation encoding="application/x-tex">{\displaystyle b}</annotation>
</semantics>
</math></span><img src="./_assets_/eb734a37dd21ce173a46342d1cc64c92/f11423fbb2e967f986e36804a8ae4271734917c3.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.338ex; width:0.998ex; height:2.176ex;" alt="{\displaystyle b}" loading="lazy"></span>, das ein Beweis der Formel … ist“) ist nicht in <b>Q</b> repräsentierbar,
weil keine seiner negativen Instanzen („die Formel … ist nicht beweisbar“) in <b>Q</b> beweisbar ist.
Es kann jedoch durch eine <a href="Arithmetische_Hierarchie" title="Arithmetische Hierarchie">Σ<sub>1</sub>-Formel</a> ausgedrückt werden,
und daher folgt aus der Σ<sub>1</sub>-Vollständigkeit von <b>Q</b>,<sup id="cite_ref-6" class="reference"><a href="#cite_note-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup>
dass jede seiner positiven Instanzen beweisbar ist.
Unter Σ<sub>1</sub>-Vollständigkeit ist hier zu verstehen,
dass jede Σ<sub>1</sub>-Aussage (der Sprache von <b>Q</b>),
die für die natürlichen Zahlen gilt,
auch in <b>Q</b> beweisbar ist.<sup id="cite_ref-7" class="reference"><a href="#cite_note-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup>
</p><p><b>Q</b> ist bereits in relativ schwachen Subtheorien von <a href="Zermelo-Fraenkel-Mengenlehre" title="Zermelo-Fraenkel-Mengenlehre">ZFC</a> interpretierbar, etwa im sogenannten Tarski-Fragment TF,<sup id="cite_ref-8" class="reference"><a href="#cite_note-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup> das nur aus folgenden drei Axiomen besteht: dem <a href="Extensionalit%C3%A4tsaxiom" title="Extensionalitätsaxiom">Extensionalitätsaxiom</a> (auch Axiom der Bestimmtheit), dem Leermengenaxiom (auch Nullmengenaxiom: die <a href="Leere_Menge" title="Leere Menge">leere Menge</a> existiert) und dem Axiom, welches für zwei Mengen <span class="mwe-math-element mwe-math-element-inline"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle x}">
<semantics>
<mrow class="MJX-TeXAtom-ORD">
<mstyle displaystyle="true" scriptlevel="0">
<mi>x</mi>
</mstyle>
</mrow>
<annotation encoding="application/x-tex">{\displaystyle x}</annotation>
</semantics>
</math></span><img src="./_assets_/eb734a37dd21ce173a46342d1cc64c92/87f9e315fd7e2ba406057a97300593c4802b53e4.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.338ex; width:1.33ex; height:1.676ex;" alt="{\displaystyle x}" loading="lazy"></span>, <span class="mwe-math-element mwe-math-element-inline"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle y}">
<semantics>
<mrow class="MJX-TeXAtom-ORD">
<mstyle displaystyle="true" scriptlevel="0">
<mi>y</mi>
</mstyle>
</mrow>
<annotation encoding="application/x-tex">{\displaystyle y}</annotation>
</semantics>
</math></span><img src="./_assets_/eb734a37dd21ce173a46342d1cc64c92/b8a6208ec717213d4317e666f1ae872e00620a0d.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.671ex; width:1.155ex; height:2.009ex;" alt="{\displaystyle y}" loading="lazy"></span> die Existenz der adjungierten Menge <span class="mwe-math-element mwe-math-element-inline"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle x\cup \{y\}}">
<semantics>
<mrow class="MJX-TeXAtom-ORD">
<mstyle displaystyle="true" scriptlevel="0">
<mi>x</mi>
<mo>∪<!-- ∪ --></mo>
<mo fence="false" stretchy="false">{</mo>
<mi>y</mi>
<mo fence="false" stretchy="false">}</mo>
</mstyle>
</mrow>
<annotation encoding="application/x-tex">{\displaystyle x\cup \{y\}}</annotation>
</semantics>
</math></span><img src="./_assets_/eb734a37dd21ce173a46342d1cc64c92/ce5d2975c9c0342bb596e561e74b7b49b6d71d2b.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:7.393ex; height:2.843ex;" alt="{\displaystyle x\cup \{y\}}" loading="lazy"></span> fordert.
</p>
<div class="mw-heading mw-heading2"><h2 id="Literatur">Literatur</h2></div>
<ul><li>A. Bezboruah, John C. Shepherdson: <cite style="font-style:italic">Gödel’s Second Incompleteness Theorem for Q</cite>. In: <cite style="font-style:italic">Journal of Symbolic Logic</cite>. <span style="white-space:nowrap">Band<span style="display:inline-block;width:.2em"> </span>41</span>, <span style="white-space:nowrap">Nr.<span style="display:inline-block;width:.2em"> </span>2</span>, 1976, <span style="white-space:nowrap">S.<span style="display:inline-block;width:.2em"> </span>503–512</span>, <a href="JSTOR" title="JSTOR">JSTOR</a>:<a rel="nofollow" class="external text" href="http://www.jstor.org/stable/2272251">2272251</a>.<span class="Z3988" title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rfr_id=info:sid/de.wikipedia.org:Robinson-Arithmetik&rft.atitle=G%C3%B6del%E2%80%99s+Second+Incompleteness+Theorem+for+Q&rft.au=A.+Bezboruah%2C+John+C.+Shepherdson&rft.date=1976&rft.genre=journal&rft.issue=2&rft.jtitle=Journal+of+Symbolic+Logic&rft.pages=503-512&rft.volume=41" style="display:none"> </span></li>
<li><a href="George_Boolos" title="George Boolos">George S. Boolos</a>, John P. Burgess, Richard C. Jeffrey: <cite style="font-style:italic">Computability and Logic</cite>. 5. Auflage. Cambridge University Press, Cambridge etc. 2007.<span class="Z3988" title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rfr_id=info:sid/de.wikipedia.org:Robinson-Arithmetik&rft.au=George+S.+Boolos%2C+John+P.+Burgess%2C+Richard+C.+Jeffrey&rft.btitle=Computability+and+Logic&rft.date=2007&rft.edition=5&rft.genre=book&rft.place=Cambridge+etc.&rft.pub=Cambridge+University+Press" style="display:none"> </span></li>
<li>Petr Hájek, Pavel Pudlák: <cite style="font-style:italic">Metamathematics of first-order arithmetic</cite>. 2. Auflage. Springer-Verlag, 1998.<span class="Z3988" title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rfr_id=info:sid/de.wikipedia.org:Robinson-Arithmetik&rft.au=Petr+H%C3%A1jek%2C+Pavel+Pudl%C3%A1k&rft.btitle=Metamathematics+of+first-order+arithmetic&rft.date=1998&rft.edition=2&rft.genre=book&rft.pub=Springer-Verlag" style="display:none"> </span></li>
<li><a href="Raphael_Robinson" title="Raphael Robinson">Raphael Robinson</a>: <cite style="font-style:italic">An Essentially Undecidable Axiom System</cite>. In: <cite style="font-style:italic">Proceedings of the International Congress of Mathematics</cite>. 1950, <span style="white-space:nowrap">S.<span style="display:inline-block;width:.2em"> </span>729–730</span>.<span class="Z3988" title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rfr_id=info:sid/de.wikipedia.org:Robinson-Arithmetik&rft.atitle=An+Essentially+Undecidable+Axiom+System&rft.au=Raphael+Robinson&rft.btitle=Proceedings+of+the+International+Congress+of+Mathematics&rft.date=1950&rft.genre=book&rft.pages=729-730" style="display:none"> </span></li>
<li><a href="Alfred_Tarski" title="Alfred Tarski">Alfred Tarski</a>, <a href="Andrzej_Mostowski" title="Andrzej Mostowski">Andrzej Mostowski</a>, <a href="Raphael_Robinson" title="Raphael Robinson">Raphael Robinson</a>: <cite style="font-style:italic">Undecidable theories</cite>. North Holland, 1953.<span class="Z3988" title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rfr_id=info:sid/de.wikipedia.org:Robinson-Arithmetik&rft.au=Alfred+Tarski%2C+Andrzej+Mostowski%2C+Raphael+Robinson&rft.btitle=Undecidable+theories&rft.date=1953&rft.genre=book&rft.pub=North+Holland" style="display:none"> </span></li>
<li><a href="Hans_Hermes" title="Hans Hermes">Hans Hermes</a>: <cite style="font-style:italic">Einführung in die mathematische Logik</cite>. 2. Auflage. B. G. Teubner Stuttgart, 1969.<span class="Z3988" title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rfr_id=info:sid/de.wikipedia.org:Robinson-Arithmetik&rft.au=Hans+Hermes&rft.btitle=Einf%C3%BChrung+in+die+mathematische+Logik&rft.date=1969&rft.edition=2.&rft.genre=book&rft.pub=B.+G.+Teubner+Stuttgart" style="display:none"> </span></li>
<li><a href="Wolfgang_Rautenberg" title="Wolfgang Rautenberg">Wolfgang Rautenberg</a>: <cite style="font-style:italic">Einführung in die Mathematische Logik</cite>. 3. Auflage. Vieweg+Teubner, Wiesbaden 2008, ISBN 978-3-8348-0578-2, <a href="Digital_Object_Identifier" title="Digital Object Identifier">doi</a>:<span class="uri-handle" style="white-space:nowrap"><a rel="nofollow" class="external text" href="https://doi.org/10.1007/978-3-8348-9530-1">10.1007/978-3-8348-9530-1</a></span>.<span class="Z3988" title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rfr_id=info:sid/de.wikipedia.org:Robinson-Arithmetik&rft.au=Wolfgang+Rautenberg&rft.btitle=Einf%C3%BChrung+in+die+Mathematische+Logik&rft.date=2008&rft.doi=10.1007%2F978-3-8348-9530-1&rft.edition=3.&rft.genre=book&rft.isbn=9783834805782&rft.place=Wiesbaden&rft.pub=Vieweg%2BTeubner" style="display:none"> </span></li>
<li>Donald Monk: <cite style="font-style:italic">Mathematical Logic</cite> (= <cite style="font-style:italic">Graduate Texts in Mathematics</cite>. <span style="white-space:nowrap">Band<span style="display:inline-block;width:.2em"> </span>37</span>). Springer, New York 1976, ISBN 0-387-90170-1.<span class="Z3988" title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rfr_id=info:sid/de.wikipedia.org:Robinson-Arithmetik&rft.au=Donald+Monk&rft.btitle=Mathematical+Logic&rft.date=1976&rft.genre=book&rft.isbn=0387901701&rft.place=New+York&rft.pub=Springer&rft.series=Graduate+Texts+in+Mathematics" style="display:none"> </span></li></ul>
<div class="mw-heading mw-heading2"><h2 id="Einzelnachweise">Einzelnachweise</h2></div>
<ol class="references">
<li id="cite_note-1"><span class="mw-cite-backlink"><a href="#cite_ref-1">↑</a></span> <span class="reference-text">Rautenberg (2008), Satz 6.4.4, S. 191</span>
</li>
<li id="cite_note-2"><span class="mw-cite-backlink"><a href="#cite_ref-2">↑</a></span> <span class="reference-text"><a href="George_Boolos" title="George Boolos">George Boolos</a>, John P. Burgess, Richard Jeffrey: <cite style="font-style:italic">Computability and Logic</cite>. 4. Auflage. Cambridge University Press, 2002, ISBN 0-521-70146-5, <span style="white-space:nowrap">S.<span style="display:inline-block;width:.2em"> </span>56</span>.<span class="Z3988" title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rfr_id=info:sid/de.wikipedia.org:Robinson-Arithmetik&rft.au=George+Boolos%2C+John+P.+Burgess%2C+Richard+Jeffrey&rft.btitle=Computability+and+Logic&rft.date=2002&rft.edition=4&rft.genre=book&rft.isbn=0521701465&rft.pages=56&rft.pub=Cambridge+University+Press" style="display:none"> </span></span>
</li>
<li id="cite_note-3"><span class="mw-cite-backlink"><a href="#cite_ref-3">↑</a></span> <span class="reference-text">W. Rautenberg (2008), S. 186.</span>
</li>
<li id="cite_note-4"><span class="mw-cite-backlink"><a href="#cite_ref-4">↑</a></span> <span class="reference-text">W. Rautenberg (2008), S. 184.</span>
</li>
<li id="cite_note-5"><span class="mw-cite-backlink"><a href="#cite_ref-5">↑</a></span> <span class="reference-text">W. Rautenberg (2008), S. 83.</span>
</li>
<li id="cite_note-6"><span class="mw-cite-backlink"><a href="#cite_ref-6">↑</a></span> <span class="reference-text">W. Rautenberg (2008), S. 190.</span>
</li>
<li id="cite_note-7"><span class="mw-cite-backlink"><a href="#cite_ref-7">↑</a></span> <span class="reference-text">W. Rautenberg (2008), S. 186.</span>
</li>
<li id="cite_note-8"><span class="mw-cite-backlink"><a href="#cite_ref-8">↑</a></span> <span class="reference-text">D. Monk (1976), S. 283–290.</span>
</li>
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