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Abstract A detailed discussion of Newtonian and general relativistic spherically symmetric dust solutions leads to the following suggested criteria for a singularity to be classified as a shell-cross : (1) All Jacobi fields have finite limits (in an orthonormal parallel propagated frame) as they approach the singularity. (2) The boundary region forms an essential C 2 singularity which is C 1 regular, that is it can be transformed away by a C 1 coordinate transformation.
Szekeres et al. (Fri,) studied this question.