References

• Schneider, Ehlers & Falco (1992), Gravitational Lenses, Springer. Multiplane lensing (§3).
• Kormann, Schneider & Bartelmann (1994), Isothermal ellipsoidal mass distributions in gravitational lensing, A&A 284. SIE deflection (§5).
• Tessore & Metcalf (2015), The elliptical power law profile lens, A&A 580, A79. EPL deflection and potential (§5).
• lenstronomy (Birrer et al.), LensModel/Profiles/epl_numba.py. The code the EPL was ported from and checked against; the point-source image finder follows the same two-step approach (§6).
• Blandford & Narayan (1986), Fermat’s principle, caustics, and the classification of gravitational lens images, ApJ 310. Arrival-time surface, image types and time delays (§4).
• Orban de Xivry & Marshall (2009), An atlas of predicted exotic gravitational lenses, MNRAS 399. Butterfly and swallowtail caustics; the Butterfly Caustic preset (§11).
• Lupton, Blanton, Fekete et al. (2004), Preparing Red-Green-Blue Images from CCD Data, PASP 116. The asinh brightness stretch (§6).
• Smith & van der Walt (2015), the matplotlib viridis, inferno and plasma colormaps; Mikhailov (2019), the Turbo colormap. The map palettes (§4), computed here from short polynomial fits after Matt Zucker’s optimized colormaps.