On the hardness of graph isomorphism

We show that the graph isomorphism problem is hard under logarithmic space many-one reductions for the complexity classes NL, PL (probabilistic logarithmic space), for every logarithmic space modular class Mod/sub k/L and for the class DET of problems NC/sup 1/ reducible to the determinant. These are the strongest existing hardness results for the graph isomorphism problem, and imply a randomized logarithmic space reduction from the perfect matching problem to graph isomorphism.