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It is one of the most important facts in 4–dimensional topology that not every
spherical homology class of a 4–manifold can be represented by an embedded sphere.
In 1978, M Freedman and R Kirby showed that in the simply connected case, many
of the obstructions to constructing such a sphere vanish if one modifies the
ambient 4–manifold by adding products of 2–spheres, a process which is
usually called stabilisation. In this paper, we extend this result to non–simply
connected 4–manifolds and show how it is related to the Spinc–bordism groups of
Eilenberg–MacLane spaces.
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