(a): Reconnection process of the double-decker filament, the nearby open field, and the emerging flux loop at the bottom. Orange and green curves represent the UF and LF, and blue the nearby open field. (b): Small post-flare loop formed by the filament lifting stretching the lower closed field and the large loop formed by the falling filament material. The bottom space is divided into three ranges to indicate the magnetic field around the filament.