diff --git a/src/fa/lc/index.tex b/src/fa/lc/index.tex index e45fb80..a5226e6 100644 --- a/src/fa/lc/index.tex +++ b/src/fa/lc/index.tex @@ -5,4 +5,5 @@ \input{./src/fa/lc/convex.tex} \input{./src/fa/lc/continuous.tex} \input{./src/fa/lc/quotient.tex} +\input{./src/fa/lc/projective.tex} \input{./src/fa/lc/hahn-banach.tex} diff --git a/src/fa/lc/projective.tex b/src/fa/lc/projective.tex new file mode 100644 index 0000000..8d5067b --- /dev/null +++ b/src/fa/lc/projective.tex @@ -0,0 +1,23 @@ +\section{Projective Limits} +\label{section:lc-projective} + + +\begin{proposition} +\label{proposition:lc-projective-topology} + Let $E$ be a vector space over $K \in \RC$, $\seqi{F}$ be locally convex spaces over $K$, and $\seqi{T}$ where $T_i \in \hom(E; F_i)$ for all $i \in I$, then the projective topology on $E$ is locally convex. +\end{proposition} +\begin{proof} + By \ref{definition:tvs-initial}, + \[ + \mathcal{B} = \bracs{\bigcap_{j \in J}T_j^{-1}(U_j) \bigg | J \subset I \text{ finite}, U_j \in \cn_{F_j}(0)} + \] + is a fundamental system of neighbourhoods at $0$. For each $i \in I$, $U_i \in \cn_{F_i}(0)$ convex, $T^{-1}(U_i)$ is also convex. Since each $F_i$ is locally convex, $\mathcal{B}$ contains a fundamental system of neighbourhoods at $0$ consisting of only convex sets. +\end{proof} + +\begin{proposition} +\label{proposition:lc-projective} + Let $(\seqi{E}, \bracsn{T^i_j|i, j \in I, i \lesssim j})$ be a downward-directed system of locally convex spaces over $K \in \RC$, then $E = \lim_{\longleftarrow}E_i$ is locally convex. +\end{proposition} +\begin{proof} + By (U) of \ref{definition:tvs-projective-limit} and \ref{definition:tvs-initial}, $E$ is equipped with the projective topology generated by the projection maps $E \to E_i$. By \ref{proposition:lc-projective-topology}, $E$ is locally convex. +\end{proof} diff --git a/src/fa/tvs/projective.tex b/src/fa/tvs/projective.tex index 06a5127..b23b0b8 100644 --- a/src/fa/tvs/projective.tex +++ b/src/fa/tvs/projective.tex @@ -1,6 +1,49 @@ \section{Projective Limits} \label{section:tvs-projective-limit} +\begin{definition}[Projective Uniformity] +\label{definition:tvs-initial} + Let $E$ be a vector space over $K \in \RC$, $\seqi{F}$ be TVSs over $K$, and $\seqi{T}$ where $T_i \in \hom(E; F_i)$ for all $i \in I$, then there exists a uniformity $\fU$ on $E$ such that: + \begin{enumerate} + \item For each $i \in I$, $T_i \in L(E; F_i)$. + \item[(U)] If $\mathfrak{V}$ is a uniformity on $E$ satisfying $(1)$, then $\mathfrak{V} \supset \fU$. + \end{enumerate} + Moreover, + \begin{enumerate} + \item[(3)] $\fU$ is translation-invariant. + \item[(4)] $E$ equipped with the topology induced by $\fU$ is a topological vector space. + \item[(5)] For any TVS $F$ over $K$ and linear map $T \in \hom(F; E)$, $T \in L(F; E)$ if and only if $T_i \circ T \in L(F; F_i)$ for all $i \in I$. + \item[(6)] The collection + \[ + \bracs{\bigcap_{j \in J}T_j^{-1}(U_j) \bigg | J \subset I \text{ finite}, U_j \in \cn_{F_j}(0)} + \] + is a fundamental system of neighbourhoods for $E$ at $0$. + \end{enumerate} + The uniformity and its induced topology are the \textbf{projective uniformity/topology} induced by $\seqi{T}$. +\end{definition} +\begin{proof} + (1), (U): By \ref{definition:initial-uniformity}. + + Let $U \in \fU$, then there exists $J \subset I$ finite and translation-invariant entourages $\seqj{U}$ such that + \[ + U \subset V = \bigcap_{j \in J}(T_j \times T_j)^{-1}(U_j) + \] + + (3): For each $j \in J$, $(x, y) \in (T_j \times T_j)^{-1}(U_j)$, and $z \in E$, + \[ + (T_j \times T_j)(x + z, y + z) = (T_jx + T_jz, T_jy + T_jz) \in U_j + \] + so $(T_j \times T_j)^{-1}(U_j)$ is translation-invariant, and so is $V$. + + (4): By (TVS1) and (TVS2), for each $j \in J$, there exists an entourage $V_j$ of $F_j$ and $\eps_j > 0$ such that for any $(x, x'), (y, y') \in V_j$ and $\lambda, \lambda' \in K$ with $\abs{\lambda - \lambda'} < \eps_j$, $(x + y, x' + y'), (\lambda x, \lambda' x') \in U_j$. + + Therefore, for any $(x, x'), (y, y') \in \bigcap_{j \in J} T_j^{-1}(V_j)$ and $\lambda, \lambda' \in K$ with $\abs{\lambda - \lambda'} < \min_{j \in J}\eps$, $(x + y, x' + y'), (\lambda x, \lambda' x') \in V$. + + (5): By \ref{definition:continuous-linear} and (4) of \ref{definition:initial-uniformity}. + + (6): By \ref{definition:initial-uniformity}. +\end{proof} + \begin{definition}[Projective Limit of Topological Vector Spaces] \label{definition:tvs-projective-limit} Let $(\seqi{E}, \bracsn{T^i_j|i, j \in I, i \lesssim j})$ be a downward-directed system of topological vector spaces over $K \in \RC$, then there exists $(E, \bracsn{T^E_i}_{i \in I})$ such that: @@ -29,9 +72,9 @@ \begin{proof} Let $(E, \bracsn{T^E_i}_{i \in I})$ be the inverse limit of $(\seqi{E}, \bracs{T^i_j|i, j \in I, i \lessim j})$ as $K$-vector spaces (\ref{proposition:module-inverse-limit}). - Equip $E$ with the initial topology generated by $\bracsn{T^E_i}_{i \in I}$, then $(E, \bracsn{T^E_i}_{i \in I})$ satisfies (1) and (2). + Equip $E$ with the projective topology generated by $\bracsn{T^E_i}_{i \in I}$, then $(E, \bracsn{T^E_i}_{i \in I})$ satisfies (1) and (2). - (4): By (5) of \ref{definition:initial-topology}. + (4): By (5) of \ref{definition:tvs-initial}. (U): By (U) of \ref{proposition:module-inverse-limit}, there exists a unique $S \in \hom(F; E)$ such that the given diagram commutes. By (4), $S \in L(F; E)$. \end{proof} diff --git a/src/topology/uniform/uc.tex b/src/topology/uniform/uc.tex index ae282f5..f9cf352 100644 --- a/src/topology/uniform/uc.tex +++ b/src/topology/uniform/uc.tex @@ -44,6 +44,7 @@ \] is a fundamental system of entourages for $\fU$. + \item[(4)] For any uniform space $Y$ and map $f: Y \to X$, $f \in UC(Y; X)$ if and only if $f_i \circ f \in UC(Y; Y_i)$ for all $i \in I$. \end{enumerate} @@ -59,6 +60,12 @@ (1): $\fU \supset (f_i \times f_i)^{-1}(\fU_i)$ for all $i \in I$. (U): For any $i \in I$, $\mathfrak{V} \supset (f_i \times f_i)^{-1}(\fU_i)$. By (F2), $\mathfrak{V} \supset \fB$, so $\mathfrak{V} \supset \fU$. + + (4): Let $J \subset I$ finite and $\seqj{U_j}$ such that $U_j \in \fU_j$ for each $j \in J$, then + \[ + (f \times f)^{-1}\paren{\bigcap_{j \in J}(f_j \times f_j)^{-1}(U_j)} = \bigcap_{j \in J}[(f_j \circ f) \times (f_j \circ f)]^{-1}(U_j) + \] + is an entourage of $Y$. \end{proof}