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We have taken the case of a circular Hα filament observed on May 9,1979 erupting into a double-ribbon flare associated with a nonspot region. The plage motions are responsible for the filament reorientation and, here as a special case, wherein the filament attains a clear circular shape before the onset of a flare. We conclude that the change in the orientation of the Hα filament marks the instability giving rise to the flare.doi:10.1007/bf02702280 fatcat:np6fymvta5bafdy3qzbhtqsuaq