Let $\kappa$ be a cardinal number with the usual order topology. We prove that all subspaces of ${\kappa }^2$ are weakly sequentially complete and, as a corollary, all subspaces of ${\omega }_1^2$ are sequentially complete. Moreover we show that a subspace of ${({\omega }_1+1)}^2$ need not be sequentially complete, but note that $X=A\times B$ is sequentially complete whenever $A$ and $B$ are subspaces of $\kappa$.

Following Kombarov we say that $X$ is $p$-sequential, for $p\in {\alpha }^{*}$, if for every non-closed subset $A$ of $X$ there is $f\in {}^{\alpha }X$ such that $f\left(\alpha \right)\subseteq A$ and $\overline{f}\left(p\right)\in X\setminus A$. This suggests the following definition due to Comfort and Savchenko, independently: $X$ is a FU($p$)-space if for every $A\subseteq X$ and every $x\in A^{-}$ there is a function $f\in {}^{\alpha }A$ such that $\overline{f}\left(p\right)=x$. It is not hard to see that $p\le {}_{RK}q$ ($\le {}_{RK}$ denotes the Rudin–Keisler order) $\iff$ every $p$-sequential space is $q$-sequential $\iff$ every FU($p$)-space is a FU($q$)-space. We generalize the spaces $S_n$ to construct examples of...

Let $X$ be a locally convex space, $m:\Sigma \to X$ be a vector measure defined on a $\sigma$-algebra $\Sigma$, and $L^1\left(m\right)$ be the associated (locally convex) space of $m$-integrable functions. Let $\Sigma \left(m\right)$ denote $\{{\chi }_{{}_E};E\in \Sigma \}$, equipped with the relative topology from $L^1\left(m\right)$. For a subalgebra $𝒜\subseteq \Sigma$, let ${𝒜}_{\sigma }$ denote the generated $\sigma$-algebra and ${\overline{𝒜}}_s$ denote the closure of $\chi \left(𝒜\right)=\{{\chi }_{{}_E};E\in 𝒜\}$ in $L^1\left(m\right)$. Sets of the form ${\overline{𝒜}}_s$ arise in criteria determining separability of $L^1\left(m\right)$; see [6]. We consider some natural questions concerning ${\overline{𝒜}}_s$ and, in particular, its relation to $\chi \left({𝒜}_{\sigma }\right)$. It is shown that...