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I am studying Peskin's An Introduction To Quantum Field Theory. On the beginning of page 284, the authors say We can turn the field [itex]\phi_S(x_1)|\phi_1\rangle=\phi_1(x_1)|\phi_1\rangle[/itex]. I tried hard to prove this relation but still can't get it right. Could anyone give me some hints? Thanks.

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# Peskin Page 284

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