Abstract: Let G be a group, let T
be an (oriented) G-tree with finite edge stabilizers,
and let VT denote the vertex set of T.
We show that, for each G-retract V'
of the G-set VT, there exists a G-tree
whose edge stabilizers are finite and
whose vertex set is V'. This fact leads to various
new consequences of the
almost stability theorem.
We also give an example of a group G, a
G-tree T and a G-retract
V' of
VT such that no G-tree has vertex set V'.
January 6, 2007 version, 15 pages, available as
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