The outer space of a free product

@inproceedings{Guirardel2005TheOS,
  title={The outer space of a free product},
  author={Vincent Guirardel and Gilbert Levitt},
  year={2005}
}
We associate a contractible ``outer space'' to any free product of groups G=G_1*...*G_q. It equals Culler-Vogtmann space when G is free, McCullough-Miller space when no G_i is Z. Our proof of contractibility (given when G is not free) is based on Skora's idea of deforming morphisms between trees. Using the action of Out(G) on this space, we show that Out(G) has finite virtual cohomological dimension, or is VFL (it has a finite index subgroup with a finite classifying space), if the groups G_i… CONTINUE READING

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