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Using stably free non-free relation modules we construct an infinite
collection of 2--dimensional homotopy types, each of
Euler-characteristic one and with trefoil fundamental group. This
provides an affirmative answer to a question asked by Berridge and
Dunwoody [J. London Math. Soc. 19 (1979) 433--436]. We also give new
examples of exotic relation modules. We show that the relation module
associated with the generating set { x, y4} for the
Baumslag--Solitar group < x, y |
xy2x-1=y3 > is stably free
non-free of rank one.
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