@article {ThVe99,
AUTHOR = {Thomas, Simon and Velickovic, Boban},
TITLE = {On the complexity of the isomorphism relation for finitely generated groups},
JOURNAL = {J. Algebra},
FJOURNAL = {Journal of Algebra},
VOLUME = {217},
YEAR = {1999},
NUMBER = {1},
PAGES = {352--373},
}