I don't have pstricks...so I am going to use words.(adsbygoogle = window.adsbygoogle || []).push({});

[tex]

\text{contraction}\{ \overline{\psi}(x_1) \psi(x_1) \}

[/tex]

My question: Propogators are usually dealing with different points...but what is the contraction of two quantities evaluated at the same point.

Thanks.

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# Dirac Contraction

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