11.10 Locally Convex Spaces of Linear Maps
Proposition 11.10.1.label Let $T$ be a set, $\sigma \subset 2^{T}$ be an ideal, $E$ be a locally convex space over $K$, and $\cf \subset E^{T}$ be a subspace such that
- (B)
For each $f \in \cf$ and $S \in \sigma$, $f(S) \subset E$ is bounded.
For each $S \in \sigma$ and continuous seminorm $\rho: E \to [0, \infty)$, let
then the $\sigma$-uniform topology on $\cf$ is induced by seminorms of the form $\rho_{S}$, where $\rho$ is a continuous seminorm on $E$, and $S \in \sigma$. In which case, the $\sigma$-uniform topology on $\cf$ is locally convex.
Proof. By Proposition 10.12.1 and Proposition 7.2.3.$\square$
Definition 11.10.2 (Saturated Ideal).label Let $E$ be a locally convex space over $K \in \RC$ and $\sigma \subset 2^{E}$ be an ideal, then $\sigma$ is saturated if:
- (1)
For each $\lambda \in K$ and $S \in \sigma$, $\lambda S \in \sigma$.
- (2)
For each $S \in \sigma$, $\ol{\aconv}(S) \in \sigma$.
For any ideal $\sigma \subset 2^{E}$, the smallest saturated ideal $\ol \sigma$ containing it is the saturated hull of $\sigma$.
Lemma 11.10.3.label Let $E$, $F$ be locally convex spaces over $K \in \RC$, $\sigma \subset 2^{E}$ be an ideal, and $\ol \sigma$ be its saturated hull, then the $\sigma$-uniformity and $\ol \sigma$-uniformity on $L(E; F)$ coincide.
Proof. Let $\tau \subset \ol \sigma$ be the collection of sets such that for each $S \in \tau$ and $U \in \cn_{F}(0)$,
is an entourage in the $\sigma$-uniformity.
For each $S \in \tau$, $U \in \cn_{F}(0)$, and $\lambda \in K$ with $\lambda \ne 0$,
is another entourage in the $\sigma$-uniformity. If $\lambda = 0$, then $N(\lambda S, U) = L(E; F)$, which is also an entourage.
Now, let $S \in \tau$ and $U \in \cn_{F}(0)$ be convex and circled, then by Proposition 5.5.3,
so $N(\ol{\aconv}(S), U)$ contains an entourage in the $\sigma$-uniformity.
Since $\tau$ is a saturated ideal that contains $\sigma$, $\tau = \ol \sigma$. Therefore the $\sigma$-uniformity and $\ol \sigma$-uniformity on $L(E; F)$ coincide.$\square$
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