geodesic equation for radial null geodesics is written in the limit of approach to the singularity, and it is shown that the occurrence of a visible singularity is equivalent to the occurrence of a positive real root for the geodesic equation, suitably written. Since this equation depends on free initial data, it follows that for a subset of the initial data there will be positive real roots and the singularity will be visible.

Null Geodesic Expansion and Cosmic Censorship
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A line of investigation which may prove useful for studying collapse of a general form of matter is to examine the evolution of the expansion $\theta$ of a congruence of outgoing null geodesics. Some preliminary work has recently been done [@the]. Consider first the case of the collapsing spherical dust cloud. If a point on the cloud ends up as a covered singularity, then $\theta$ at this point evolves to a negative value, as expected, starting from its initial positive value. A naked singularity forms precisely in those cases for which the initially positive $\theta$ continues to remain positive all the way until singularity formation. We have given an argument suggesting that this property of $\theta$ (i.e. its remaining positive 