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It is well-known that $\mathcal{C}[0,1]$, the space consisting of all scalar-valued continuous functions over the unit interval, has a monotone Schauder basis. In fact, we can construct such a basis from a countable dense subset, say $D$, of $[0,1]$, and considering the projections that, given $F\subseteq D$ finite, map a function $f\in \mathcal{C}[0,1]$ into the piecewise linear function with nodes in $(x,f(x))$, $x\in F$.

Unfortunately, this canonical basis is not bimonotone. Is there such a basis for $\mathcal{C}[0,1]$? Note that a positive answer would imply that any weakly null sequence in any Banach space would have an approximately bimonotone subsequence.

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2 Answers 2

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No, because the Schauder basis for $C[0,1]$ is perfectly reproducible. See the second paper by Lindenstrauss and Pełczyński, Contributions to the Theory of the Classical Banach Spaces, J. Functional Analysis 8 (1971) 225–249, https://doi.org/10.1016/0022-1236(71)90011-5

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  • $\begingroup$ Thank you so much for answering me, Bill. $\endgroup$
    – Anso
    Commented Mar 24, 2023 at 20:26
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The space $C[0,1]$ has the Daugavet property; in particular, for a finite-rank projection $\|I-P\|=1+\|P\|$, which equals $2$ if $\|P\|=1$.

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