Lens-system configurations of the three degenerate 3L1S solutions. For each solution, the lower panel shows the source trajectory, marked by an arrowed line, with respect to the caustic, and the upper panel shows the trajectory with respect to the positions of the lens components, marked by blue dots with labels M₁, M₁, and M₃. The gray curves encompassing the caustic in the lower panels represent equi-magnification contours. The dashed circles in the upper panels represent the Einstein ring.