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A subspace $Y$ of $X$ is said to be semi M-ideal if $\exists$ a projection $P$ (not necessarily linear) from $X^*$ to $Y^\perp$ such that $\|x^*\|=\|Px^*\|+\|x^*-Px^*\|$. And also, $P(\lambda x^*+Py^* …

Yes, because $(B_{X^*},w^*)$ is compact metrizable. So $x^{**}$ is $w^*$-continuous at any $x^*\in B_{X^*}$.

This function is weakly continuous almost everywhere. One can show that $f$ is Riemann Int. over $[0,1]$. Now if the value of this integral is $x$, for some $x\in \ell_\infty[0,1]$, then for any $x^* …

A subspace $Y$ of a Banach space is said to be Hahn-Banach smooth if every $f\in Y^*$ has unique norm preserving extension to whole $X$. This notion is related to many other geometric properties of Ba …

Does there exist a Banach space $X$ such that $X^{**}$ is separable but $X^{***}$ is non-separable? More generally, for every natural $n$ can someone construct an example of Banach space $X$ such tha …

Can someone please tell me the brief sketch (or any known reference) of the following results? Why $\ell_2$ is finitely representable in any infinite-dimensional Banach space? Why every Banach spac …

Let $C[0,1]$ be the space of all Real valued continuous functions on $[0,1]$ with the usual supremum norm. Does there exist an equivalent renorming on $C[0,1]$ such that the corresponding dual norm is …

A Banach space is said to have Krein-Milman property (KMP in short) if every closed bounded convex set of it is a closed convex hull of its extreme points. Eg. Any reflexive space has KMP, $\ell_1$ ha …

Let $M^+(D)$ be the space of all positive measures on a closed convex subset $D$ of a locally convex topological vector space $E$. Two measure $\mu, \nu\in M^+(D)$ one can define a partial ordering $\ …

I have two problems to ask. Let $A$ be a function algebra of $C(K)$. $t\in K$ is said to be a peak point of $A$ if $\exists~f\in A$ s.t. $|f(t)|=\|f\|$ and $|f(s)|<|f(t)|$ for any $s\neq t$. Suppos …

Let us recall Phelp's property-$U$: A subspace $Y\subset X$ is said to have property-$U$ if every $y^*\in Y^*$ has unique norm preserving extension over $X$. $Y$ is weak Hahn-Banach smooth if $y^*$ ha …

The problem that I posted was a much generalized form of what I had in my mind. All I want to know the literature of Hahn-Banach type extension of Lipschitz map. I know only about the result by Kirszb …

Solution (1). Let $A=\{f\in A(\mathbb{D}):f(0)=f(1)\}$. It follows from the Maximum Modulus Principle that the Choquet boundary $Ch(A)$ does not contain $1$, as $B(A)$ and the set of peak points are …

A Banach space $X$ is said to be Hahn-Banach smooth if every linear functional on $X$ has a unique norm-preserving extension over $X^{**}$. Weak Hahn-Banach smoothness is what if the above condition h …

Let $K$ be a compact Hausdorff space and $A$ be a subset of $C(K)$. $A$ is said to be a Korovkin set if for every sequence $(T_n)$ of positive linear operators on $C(K)$, the condition $\|T_n(f)- f\|_ …