Lens system configuration corresponding to the best-fit 2L1S model. The cuspy closed red figure represents the caustic, while the two blue dots labeled M₁ and M₂ denote the positions of the binary-lens components. The arrowed line illustrates the trajectory of the source. The four empty circles, scaled to the source size, mark the source positions along its trajectory at the times corresponding to the anomaly features at t₁, t₂, t₄, and t₅. The gray curves surrounding the caustic represent the equi-magnification contours.