We discuss the contribution to the characteristic lensing quantities. i.e.,
the deflection angle and Einstein radius, due to the higher-order terms (e
.g., the gravitomagnetic terms) considered in the lens potential. The cases
we analyze are the singular isothermal sphere and the disk of spiral galax
ies. It is possible to see that the perturbative effects could be of the or
der 10(-3) with respect to the ordinary terms of weak field and thin lens a
pproximations, so that it is not a far hypothesis to obtain evidences of th
em in a next future by suitable experiments. (C) 2001 Elsevier Science B.V.
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