Gi and CoNp



Hi,

reading in this paper:
http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.36.9811
on page 48 proposition 3.31 is written that GI (graph isomorphism)
reduces to FI (formula isomorphism) but FI is coNp-Hard,
so why this relationship is not enough to proof that GI is in CoNp?

thanks a lot
Regards
FC


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