  We study an eruptive X1.1 circular-ribbon flare on 2013 November 10,
combining multiwavelength observations with a coronal field reconstruction
using a non-force-free field method. In the first stage, a filament forms via
magnetic reconnection between two mildly twisted sheared arcades, which are
embedded under the fan dome associated with a null point. This reconnection
seems to be driven by photospheric shearing and converging flows around the
inner two arcade footpoints, consistent with the flare-related changes of
transverse field. The southern portion of the filament rises upward due to
torus instability and pushes against the null point. The induced null point
reconnection then generates the circular ribbon and the initial remote
brightening in the west, as accelerated electrons precipitate along the fan and
propagate outward along quasi-separatix surfaces with high values of the
squashing factor (Q) in the envelope fields, which have a curtain-like shape
here. In the second stage, the southern end of the flux rope breaks away from
the surface, sequentially disrupts the dome and overlying fields, and erupts in
a whipping-like fashion to become a partial halo coronal mass ejection. This
leads to an enhanced flare emission and fast-moving remote brightenings at the
footpoints of the magnetic curtain, which span a remarkably broad region and
are also associated with coronal dimmings. This is a rare example of eruptive
circular-ribbon flares, in which the evolution of a flux rope from its
formation to successful eruption out of the dome and the resulting unusually
extended remote brightenings are completely observed.
