Abstract:
The semilattice of $G$-compactifications of a $G$-Tikhonov space $X$ is studied. The question of what sets containing $X$ and contained in the maximal $G$-compactification $\beta_GX$ must be contained also in all other $G$-compactifications of $X$ is considered. Conditions for $\beta_GX$ to be the completion of the $G$-space $X$ with respect to a natural uniformity (proximity) on $X$ are obtained. Sufficient conditions for the existence of a smallest (minimal, unique) $G$-compactification of $X$ are given.