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A Banach space is a complete normed vector space: A vector space equipped with a norm such that every Cauchy sequence converges.

13 votes
2 answers
905 views

Does $X$ embed in $Y$, and $Y$ embed in $X$, always imply that $X$ isomorphic onto $Y$?

Let $X$ and $Y$ be Banach spaces. The notion of the embedded spaces was introduced by D.S. Djordjevic. Say that $X$ embed in $Y$, and write $X \preceq Y$, if there exists a left invertible operator $ …
Qingping Zeng's user avatar
6 votes
0 answers
257 views

What is the intersection of the closures of left invertible operators and right invertible o...

From Douglas Zare's answer (see Does $X$ embed in $Y$, and $Y$ embed in $X$, always imply that $X$ isomorphic onto $Y$?), one know that $$ \overline{G_{l}(X,Y)} \bigcap \overline{G_{r}(X,Y) } = \ove …
Qingping Zeng's user avatar
0 votes

A separable Banach space and a non-separable Banach space having the same dual space?

To the best of my knowledge, among classical Banach spaces, $c_0,$ C[a,b], $L_1[a,b],$ $l_{\infty}/c_0$ are not dual.
Qingping Zeng's user avatar