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[parent] $T_f$ is a distribution of zeroth order (Proof)

To check that $ T_f$ is a distribution of zeroth order, we shall use condition (3) on this page. First, it is clear that $ T_f$ is a linear mapping. To see that $ T_f$ is continuous, suppose $ K$ is a compact set in $ U$ and $ u\in \mathcal{D}_K$, i.e., $ u$ is a smooth function with support in $ K$. We then have

$\displaystyle \vert T_f(u)\vert$ $\displaystyle =$ $\displaystyle \vert\int_K f(x) u(x) dx \vert$  
  $\displaystyle \le$ $\displaystyle \int_K \vert f(x)\vert \,\, \vert u(x)\vert dx$  
  $\displaystyle \le$ $\displaystyle \int_K \vert f(x)\vert dx \, \vert\vert u\vert\vert _\infty.$  

Since $ f$ is locally integrable, it follows that $ C=\int_K \vert f(x)\vert dx$ is finite, so
$\displaystyle \vert T_f(u)\vert \le C \vert\vert u\vert\vert _\infty.$
Thus $ f$ is a distribution of zeroth order ([1], pp. 381). $ \Box$

References

1
S. Lang, Analysis II, Addison-Wesley Publishing Company Inc., 1969.



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Cross-references: order, distribution, finite, support, smooth function, compact set, continuous, linear mapping, clear
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This is version 3 of $T_f$ is a distribution of zeroth order, born on 2003-07-09, modified 2003-12-20.
Object id is 4434, canonical name is T_fIsADistributionOfZerothOrder.
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Classification:
AMS MSC46F05 (Functional analysis :: Distributions, generalized functions, distribution spaces :: Topological linear spaces of test functions, distributions and ultradistributions)
 46-00 (Functional analysis :: General reference works )

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