# A note on the hardness of tree isomorphism

@article{Jenner1998ANO, title={A note on the hardness of tree isomorphism}, author={Birgit Jenner and Pierre McKenzie and Jacobo Tor{\'a}n}, journal={Proceedings. Thirteenth Annual IEEE Conference on Computational Complexity (Formerly: Structure in Complexity Theory Conference) (Cat. No.98CB36247)}, year={1998}, pages={101-105} }

We prove that the tree isomorphism problem, when trees are encoded as strings, is NC/sup 1/-hard under DLOGTIME-reductions. NC/sup 1/-completeness thus follows from Buss's recent NC/sup 1/ upper bound. By contrast, we prove that testing isomorphism of two trees encoded as pointer lists is L-complete.

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