## Miroslav Zelen\'y

*Sets of extended uniqueness and $\sigma $-porosity *

Comment.Math.Univ.Carolinae 38,2 (1997) 337-341. **Abstract:**We show that there exists a closed non-$\sigma $-porous set of extended uniqueness. We also give a new proof of Lyons' theorem, which shows that the class of $H^{(n)}$-sets is not large in $U_0$.

**Keywords:** $\sigma $-porosity, sets of extended uniqueness, trigonometric series, $H^{(n)}$-sets

**AMS Subject Classification:** Primary 42A63

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