On some classes of Lindelöf Sigma-spaces

Abstract

We consider special subclasses of the class of Lindelöf Sigma-spaces obtained by imposing restrictions on the weight of the elements of compact covers that admit countable networks: A space $X$ is in the class $LΣ(\leqκ)$ if it admits a cover by compact subspaces of weight $κ$ and a countable network for the cover. We restrict our attention to $κ\leqω$. In the case $κ=ω$, the class includes the class of metrizably fibered spaces considered by Tkachuk, and the $P$-approximable spaces considered by Tkacenko. The case $κ=1$ corresponds to the spaces of countable network weight, but even the case $κ=2$ gives rise to a nontrivial class of spaces. The relation of known classes of compact spaces to these classes is considered. It is shown that not every Corson compact of weight $\aleph_1$ is in the class $LΣ(\leq ω)$, answering a question of Tkachuk. As well, we study whether certain compact spaces in $LΣ(\leqω)$ have dense metrizable subspaces, partially answering a question of Tkacenko. Other interesting results and examples are obtained, and we conclude the paper with a number of open questions.