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Power-law inflation is cosmic inflation with a scale factor proportional to $t^p$ for constant $p>1$. Its Hubble parameter is $H=p/t$ and its first Hubble slow-roll parameter is ${ϵ}_H=1/p$. The comoving Hubble radius decreases as $t^{1-p}$. A canonical inflaton with an exponential inflaton potential admits an exact example. Because ${ϵ}_H$ is constant, an indefinitely maintained power law has no graceful exit from inflation.