I downloaded genus2reduction from 

           http://www.math.u-bordeaux.fr/~liu/G2R/

with the permission of Q. Liu:

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From Qing.Liu@math.u-bordeaux1.fr Sat Jul 16 23:33:18 2005
Return-path: <Qing.Liu@math.u-bordeaux1.fr>

Hi William,

It will be a pleasure for me that you include genus2reduction in SAGE.
Note however that the program is not maintained anymore.  Please
feel free to make any technical modifications to make it compile
in recent systems.

Best regards,

Liu
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Changes needed to make it work with latest PARI C library, etc.

