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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def fom(reco, true_image):
 """Sobolev type FoM enforcing both gradient and absolute similarity."""

    gradient = odl.Gradient(reco.space)
    return (gradient(reco - true_image).norm() +
            reco.space.dist(reco, true_image))