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I was reading through the section on path integrals in Srednicki's QFT book. I came across equation 6.22

[tex]\langle 0|0\rangle_{f,h} = \int\mathcal{D}p\mathcal{D}q\exp{\left[i\int_{-\infty}^{\infty}dt\left(p\dot{q}-H_{0}(p,q)-H_{1}(p,q)+fq+hp\right)\right]}[/tex]

[tex]= \exp{\left[-i\int_{-\infty}^{\infty}dt H_{1}\left(\frac{1}{i}\frac{\delta}{\delta h(t)},\frac{1}{i}\frac{\delta}{\delta f(t)}\right)\right]}\times\int\mathcal{D}q\mathcal{D}p\exp{\left[i\int_{-\infty}^{\infty}dt(p\dot{q}-H_{0}(p,q)+fq+hp)\right]}[/tex]

How did we get the second line of the equation?

PS -- f and h are differentiable functions of time, used just to pull down suitable powers of q and p.

Thanks in advance.

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# Srednicki Path Integrals eq 6.22

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