On the size of quotients of function spaces on a topological group

Ahmed Bouziad ; Mahmoud Filali

Studia Mathematica, Tome 204 (2011), p. 243-259 / Harvested from The Polish Digital Mathematics Library

Résumé

For a non-precompact topological group G, we consider the space C(G) of bounded, continuous, scalar-valued functions on G with the supremum norm, together with the subspace LMC(G) of left multiplicatively continuous functions, the subspace LUC(G) of left norm continuous functions, and the subspace WAP(G) of weakly almost periodic functions. We establish that the quotient space LUC(G)/WAP(G) contains a linear isometric copy of $ℓ_{∞}$, and that the quotient space C(G)/LMC(G) (and a fortiori C(G)/LUC(G)) contains a linear isometric copy of $ℓ_{∞}$ when G is a normal non-P-group. When G is not a P-group but not necessarily normal we prove that the quotient is non-separable. For non-discrete P-groups, the quotient may sometimes be trivial and sometimes non-separable. When G is locally compact, we show that the quotient space LUC(G)/WAP(G) contains a linear isometric copy of $ℓ_{∞}(κ(G))$, where κ(G) is the minimal number of compact sets needed to cover G. This leads to the extreme non-Arens regularity of the group algebra L¹(G) when in addition either κ(G) is greater than or equal to the smallest cardinality of an open base at the identity e of G, or G is metrizable. These results are improvements and generalizations of theorems proved by various authors along the last 35 years and until very recently.

Détail

Publié le : 2011-01-01

Zbl 1234.43001

EUDML-ID : urn:eudml:doc:286643