A study was made of the relationship between the symmetry group of a crystalline body and the line singularities, in the deformation field, which the material could support. A method was developed which, in some cases, permitted the description of a singularity by means of a suitable DeRham current, supported by the defect sub-manifold. This current was a measure of obstruction to the extension of the local deformation to a globally-defined field. The present procedure was the basis of a formulation of the weak-field equations for a defective material. It clarified the structure of the compatibility relationships for almost any class of material symmetry.

Material Symmetry and Singularities in Solids. P.Cermelli: Proceedings of the Royal Society, 1999, 455[1981], 299-322