  Let ell be a prime, and H a curve of genus 2 over a field k of characteristic
not 2 or ell. If S is a maximal Weil-isotropic subgroup of Jac(H)[ell], then
Jac(H)/S is isomorphic to the Jacobian of some (possibly reducible) curve X. We
investigate the Dolgachev--Lehavi method for constructing the curve X,
simplifying their approach and making it more explicit. The result, at least
for ell=3, is an efficient and easily programmable algorithm suitable for
number-theoretic calculations.
