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Continuous Linear Functionals

Why

We can characterize the continuous linear functionals.

Main result

Let $F$ be a linear functional on a normed space $(V, \norm{\cdot })$. The following are equivalent:
  1. $F$ is continuous;
  2. $F$ is continuous at 0;
  3. $\sup_{\norm{x} \leq 1}\set{\abs{F(x)}} < \infty$.1
For this reason we often call continuous linear functionals the bounded linear functionals or call them continuous bounded linear functionals.
  1. Future editions will include an account, and that will fill out this sheet. ↩︎
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