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Let $X$ and $Y$ be locally convex spaces and let $T \colon X \rightarrow Y$ be a linear mapping. The adjoint of $T$ is an operator $T^{\prime} \colon D(T^{\prime}) \rightarrow X^{\star}$ where $D(T^{\prime}) = ( y^{\star} \in Y^{\star} \colon y^{\star}T \in X^{\star})$ given by $T^{\prime}y^{\star}= y^{\star}T$.

When

Let $X$ is be an infra-barreled LCS and let $Y$ is be a LCS. If we assume that $(X, \tau)$ is a K-space for some compatible topology (i.e. $\sigma(X, X^{\star}) \subset \tau \subset \beta(X, X^{\star})$) and $D(T^{\prime}) = Y^{\star}$ . Then then $T$ is continuous with respect to the original topology of $X$.

(Reference: Theorem 3 in Endre Pap, Charles Swartz, A Locally Convex Version of Adjoint Theorem)

Definition 1

If $(X, \tau)$ is TVS, a sequence $(x_n)$ in $X$ is said to be a $\tau - K$-sequence if every subsequence of $(x_n)$ has a further subsequence $(x_{n_k})$ such that the subseries $\sum x_{n_k}$ is $\tau$-convergent to an element of $E$.

Definition 2

A topological vector space $(X, \tau)$ is said to be $K$-space if every sequence which converges to $0$ is a $\tau - K$-sequence.

Definition 3

A locally convex vector space $X$ is called infra-barreled if every bound absorbing barrel (i.e. a barrel absorbing all bounded sets in $X$) in $X$ is a neighborhood of $0$.

Question

I was wondering what should we assume on $X$ and $Y$ to get a continuous linear mapping $T$ when we have that $T^{\prime}$ is continuous (in its strong topology).

The problem is quite obvious when $X$ and $Y$ are normed spaces - so I'm not interested in this case.

In case of LCS: If $T$ is continuous then $T^{\prime}$ is also continuous (cos I assumed that $D(T)=X$) and D(T)=X$), what about the converseis true if$D(T^{\prime})=Y^{\star}$and$X$,$Y$are reflexive spaces, but reflexivity is a very strong assumption. ? Thank you in advance for any help and references. BTW. I have a problem with { } brackets in LaTeX environment so I used ( ). 3 added 44 characters in body Before my main question let me start with the following notions. Let$X$and$Y$be locally convex spaces and let$T \colon X \rightarrow Y$be a linear mapping. The adjoint of$T$is an operator$T^{\prime} \colon D(T^{\prime}) \rightarrow X^{\star}$where$D(T^{\prime}) = ( y^{\star} \in Y^{\star} \colon y^{\star}T \in X^{\star})$given by$T^{\prime}y^{\star}= y^{\star}T$. When$X$is an infra-barreled LCS and$Y$is a LCS. If we assume that$(X, \tau)$is a K-space for some compatible topology (i.e.$\sigma(X, X^{\star}) \subset \tau \subset \beta(X, X^{\star})$) and$D(T^{\prime}) = Y^{\star}$. Then$T$is continuous with respect to the original topology of$X$. (Reference: Theorem 3 in Endre Pap, Charles Swartz, A Locally Convex Version of Adjoint Theorem) Definition 1 If$(X, \tau)$is TVS, a sequence$(x_n)$in$X$is said to be a$\tau - K$-sequence if every subsequence of$(x_n)$has a further subsequence$(x_{n_k})$such that the subseries$\sum x_{n_k}$is$\tau$-convergent to an element of$E$. Definition 2 A topological vector space$(X, \tau)$is said to be$K$-space if every sequence which converges to$0$is a$\tau - K$-sequence. Definition 3 A locally convex vector space$X$is called infra-barreled if every bound absorbing barrel (i.e. a barrel absorbing all bounded sets in$X$) in$X$is a neighborhood of$0$. Question I was wondering what should we assume on$X$and$Y$to get a continuous linear mapping$T$when we have that$T^{\prime}$is continuous (in its strong topology). The problem is quite obvious when$X$and$Y$are normed spaces - so I'm not interested in this case. If$T$is continuous then$T^{\prime}$is also continuous (cos I assumed that$D(T)=X$) and the converse is true if$D(T^{\prime})=Y^{\star}$and$X$,$Y$are reflexive spaces, but reflexivity is a very strong assumption. Thank you in advance for any help and references. BTW. I have a problem with { } brackets in LaTeX environment so I used ( ). 2 added 182 characters in body; edited body Before my main question let me start with the following notions. Let$X$and$Y$be locally convex spaces and let$T \colon X \rightarrow Y$be a linear mapping. The adjoint of$T$is an operator$T^{\prime} \colon D(T^{\prime}) \rightarrow X^{\star}$where$D(T^{\prime}) = ( y^{\star} \in Y^{\star} \colon y^{\star}T \in X^{\star})$given by$T^{\prime}y^{\star}= y^{\star}T$. When$X$is an infra-barreled LCS and$Y$is a LCS. If we assume that$(X, \tau)$is a K-space for some compatible topology (i.e.$\sigma(X, X^{\star}) \subset \tau \subset \beta(X, X^{\star})$) and$D(T^{\prime}) = Y^{\star}$. Then$T$is continuous with respect to the original topology of$X$. (Reference: Theorem 3 in Endre Pap, Charles Swartz, A Locally Convex Version of Adjoint Theorem) Definition 1 If$(X, \tau)$is TVS, a sequence$(x_n)$in$X$is said to be a$\tau - K$-sequence if every subsequence of$(x_n)$has a further subsequence$(x_{n_k})$such that the subseries$\sum x_{n_k}$is$\tau$-convergent to an element of$E$. Definition 2 A topological vector space$(X, \tau)$is said to be$K$-space if every sequence which converges to$0$is a$\tau - K$-sequence. Definition 3 A locally convex vector space$X$is called infra-barreled if every bound absorbing barrel (i.e. a barrel absorbing all bounded sets in$X$) in$X$is a neighborhood of$0$. Question I was wondering what should we assume on$X$and$Y$to get a continuous linear mapping$T$when we have that$T^{\prime}$is continuous (in its strong topology). The problem is quite obvious when$X$and$Y$are normed spaces - so I'm not interested in this case. If$T$is continuous then$T^{\prime}$is also continuous (cos I assumed that$D(T)=X$) and the converse is true if$D(T^{\prime})=Y^{\star}$and$X$,$Y\$ are reflexive spaces.

Thank you in advance for any help and references.

BTW. I have a problem with { } brackets in LaTeX environment so I used ( ).

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