Topology of linked defects in condensed matter

The present paper contains a systematic study of several linked singularities in condensed matter. We introduce a hierarchy of conservation laws in terms of differential forms corresponding to a sequence of linking invariants so that we can distinguish nontrivial links possessing zero Gauss linking coefficients. We obtain a set of topological obstruction rules for links in nematics, cholesterics, and superfluid³He and⁴He.