Before revision:  More importantly, our analysis uncovers a gap in Khuller et al.'s proof for the extensively mentioned approximation factor of (1-1/\mathrm{e})\approx 0.393 in the literature to clarify a long time of misunderstanding on this issue.
After revision:  More importantly, our analysis closes a gap in Khuller et al.'s proof for the extensively mentioned approximation factor of (1-1/\mathrm{e})\approx 0.393 in the literature to clarify a long time of misunderstanding on this issue.