quantum field theory - Wick's theorem and Feynman propagator

(this is the image from book 'No nonsense QFT' by Jakob Schwichtenberg, page no, 426) The quantity $[\phi_-(x),\phi_+(y)]$ is like an operator inside the bra-kets $\langle 0|$ and $|0\rangle$. I'm

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Quantum field theory by Washington Soares Alves - Issuu

Propagator derivations – Quantum field theory

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SOLUTION: Quantum field theory example sheet 4 - Studypool

Peeter Joot's Blog » PHY2403H Quantum Field Theory. Lecture 15b

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Sam Walters ☕️ on X: In #quantum field theory, the #Feynman