Almost paratopological groups

Abstract

A class of almost paratopological groups is introduced, which (1) contains paratopological groups and Hausdorff quasitopological groups; (2) is closed under products; (3) subgroups. Almost paratopological $T_1$ groups $G$ are characterized by the fact that $\{(x,y)\in G^2:xy=e\}$ is closed in $G^2$. A compact almost paratopological group is topological. A regular $\Sigma$-space with a countable extend and a separately continuous Mal'tsev operation is $\omega$-cellular (and ccc). A $\sigma$-compact regular almost paratopological group is ccc. In particular, a $\sigma$-compact regular quasitopological group is ccc.