Before revision:  Compared with the existing algorithm } for constructing source-wise round-trip spanners }\hspace{0pt}%DIFAUXCMD } , our algorithm significantly improves their construction time \Omega(\min\{ms,n^\omega\})
After revision:  Compared with the existing algorithm } for constructing source-wise round-trip spanners \mbox{%DIFAUXCMD \cite{ZL17}\hspace{0pt}%DIFAUXCMD } , our algorithm significantly improves their construction time \Omega(\min\{ms,n^\omega\})