Abstract:
We define $\Delta$-Baire spaces. If a paratopological group $G$ is $\Delta$-Baire space,
then $G$ is a topological group. Locally pseudocompact spaces, Baire $p$-spaces, Baire $\Sigma$-spaces,
products of Čech-complete spaces are $\Delta$-Baire spaces.
Key words:paratopological groups, semi-topological groups, continuity of the inverse, Baire spaces, $\Delta$-Baire spaces.