Relatively open operators and the ubiquitous concept
- Autores: R. W. Cross
- Localización: Publicacions matematiques, ISSN 0214-1493, Vol. 38, Nº 1, 1994, págs. 69-79
- Idioma: inglés
- DOI: 10.5565/publmat_38194_07
- Títulos paralelos:
- Operadores relativamente abiertos y concepto de ubicuidad
- Enlaces
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Resumen
A linear operator $T:D(T)\subset X\rightarrow Y$, when $X$ and $Y$ are normed spaces, is called ubiquitously open (UO) if every infinite dimensional subspace $M$ of $D(T)$ contains another such subspace $N$ for which $T|N$ is open (in the relative sense). The following properties are shown to be equivalent: (i) $T$ is UO, (ii) $T$ is ubiquitously almost open, (iii) no infinite dimensional restriction of $T$ is injective and precompact, (iv) either $T$ is upper semi-Fredholm or $T$ has finite dimensional range, (v) for each infinite dimensional subspace $M$ of $D(T)$, we have $\dim (T|M)^{-1}(0)+\Delta (T|M)>0$. In case $T$ is closed and $X$ and $Y$ are Banach spaces, $T$ is UO if and only if $\overline{TM}\subset T\overline{M}$ for every linear subspace $M$ of $X$.
