Cobordisms of semi-boundary links

AbstractA new invariant of link concordance is introduced, which takes values in the homotopy groups of the 2-sphere and which vanishes for links concordant to boundary links. When the category of links is broadened to allow manifold (i.e. non-spherical) links and the equivalence relation of concordance is weakened to β-equivalence, this invariant is shown to completely answer the question of which links are β-equivalent to boundary links