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Note on bi-Lipschitz embeddings into normed spaces

Jiří Matoušek (1992)

Commentationes Mathematicae Universitatis Carolinae

Let ( X , d ) , ( Y , ρ ) be metric spaces and f : X Y an injective mapping. We put f Lip = sup { ρ ( f ( x ) , f ( y ) ) / d ( x , y ) ; x , y X , x y } , and dist ( f ) = f Lip . f - 1 Lip (the distortion of the mapping f ). We investigate the minimum dimension N such that every n -point metric space can be embedded into the space N with a prescribed distortion D . We obtain that this is possible for N C ( log n ) 2 n 3 / D , where C is a suitable absolute constant. This improves a result of Johnson, Lindenstrauss and Schechtman [JLS87] (with a simpler proof). Related results for embeddability into p N are obtained by a similar method.

Note on countable unions of Corson countably compact spaces

Ondřej F. K. Kalenda (2004)

Commentationes Mathematicae Universitatis Carolinae

We show that a compact space K has a dense set of G δ points if it can be covered by countably many Corson countably compact spaces. If these Corson countably compact spaces may be chosen to be dense in K , then K is even Corson.

Note on dense covers in the category of locales

Jan Paseka (1994)

Commentationes Mathematicae Universitatis Carolinae

In this note we are going to study dense covers in the category of locales. We shall show that any product of finitely regular locales with some dense covering property has this property as well.

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