The fixed group of an automorphism of a word hyperbolic group is rational.
Neumann, Walter D.
Inventiones mathematicae, Tome 110 (1992), p. 147-150 / Harvested from Göttinger Digitalisierungszentrum
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Publié le : 1992-01-01
EUDML-ID : urn:eudml:doc:144046 
@article{GDZPPN002110237,
     title = {The fixed group of an automorphism of a word hyperbolic group is rational.},
     journal = {Inventiones mathematicae},
     volume = {110},
     year = {1992},
     pages = {147-150},
     zbl = {0793.20033},
     url = {http://dml.mathdoc.fr/item/GDZPPN002110237}
}

Neumann, Walter D. The fixed group of an automorphism of a word hyperbolic group is rational.. Inventiones mathematicae, Tome 110 (1992) pp. 147-150. http://gdmltest.u-ga.fr/item/GDZPPN002110237/