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	<entry>
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		<title>Wu–Sprung potential</title>
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		<summary type="html">&lt;p&gt;70.192.84.95: Correct spelling &amp;quot;interpretate&amp;quot; to &amp;quot;interpret&amp;quot;&lt;/p&gt;
&lt;hr /&gt;
&lt;div&gt;The &#039;&#039;&#039;Plebanski tensor&#039;&#039;&#039; is a [[tensor rank|rank 4 tensor]] in [[general relativity]] constructed from the [[trace-free Ricci tensor]].  It was first defined by [[Jerzy Plebański]] in 1964.&amp;lt;ref&amp;gt;{{citation|first1=J.|last1=Plebański|title=|journal=Acta Phys. Polon.|volume=26|page=963|year=1964}}&amp;lt;/ref&amp;gt;&lt;br /&gt;
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Let &amp;lt;math&amp;gt;S_{ab}&amp;lt;/math&amp;gt; be the trace-free Ricci tensor:&lt;br /&gt;
&lt;br /&gt;
:&amp;lt;math&amp;gt;S_{ab}=R_{ab}-\frac{1}{4}Rg_{ab}.&amp;lt;/math&amp;gt;&lt;br /&gt;
&lt;br /&gt;
Then the Plebanski tensor is defined as&lt;br /&gt;
&lt;br /&gt;
:&amp;lt;math&amp;gt;P^{ab}{}_{cd}=S^{[a}{}_{[c}S^{b]}{}_{d]}+\delta^{[a}{}_{[c}S^{b]e}S_{d]e}-\frac{1}{6}\delta^{[a}{}_{[c}\delta^{b]}{}_{d]}S^{ef}S_{ef}.&amp;lt;/math&amp;gt;&lt;br /&gt;
&lt;br /&gt;
The advantage of the Plebanski tensor is that it shares the same symmetries as the [[Weyl tensor]].  It therefore becomes possible to classify different [[spacetime]]s based on additional algebraic symmetries of the Plebanski tensor in a manner analogous to the [[Petrov classification]].&amp;lt;ref&amp;gt;{{citation|first1=C. B. G.|last1=McIntosh|first2=J. M.|last2=Foyster|first3=A. W.-C.|last3=Lun|title=The classification of the Ricci and Plebanski tensors in general relativity using Newman-Penrose formalism|journal=J. Math. Phys.|volume=22|page=2620|year=1981|doi=10.1063/1.524840|bibcode = 1981JMP....22.2620M }}&amp;lt;/ref&amp;gt;&lt;br /&gt;
&lt;br /&gt;
==References==&lt;br /&gt;
&amp;lt;references/&amp;gt;&lt;br /&gt;
&lt;br /&gt;
&lt;br /&gt;
[[Category:Tensors]]&lt;br /&gt;
&lt;br /&gt;
&lt;br /&gt;
&lt;br /&gt;
{{relativity-stub}}&lt;/div&gt;</summary>
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