Eruption process of the flare-driving filament. Panels a and b demonstrate the snapshots of the filament eruption seen in SDO/AIA 304 Å and STEREO-A/EUVI 304 Å, respectively. Panel c shows the time-distance stack plot of the AIA 304 Å intensities along the slice drawn in panel a. Panel d displays the velocity evolution of the filament leading edge along the selected slice, which is traced by the filled circles plotted in panel c. The vertical dashed lines in panel d divide the eruption process into three stages.