A contour plot of positive iso- J curves is shown for a gravitational binary lens \epsilon _ { 2 } = 0.1883 and \ell = 0.687 .
The caustic curve is made of 4-cusped central caustic ( so-called “ stealth bomber ” ) on the lens axis and two triangular caustics off the lens axis .
The cusps of the trioids are all negative cusps .
The positive image magnification contours outside the positive cusps on the lens axis are elongated along the symmetry axis .
It is in contrast with figure 4 of astro-ph/0206162 ( Gaudi and Petters ) where the contours appear to contract along the symmetry axis .
We apologize if our citation of their figure 4 without the caution played any role of causing confusion with readers .