analysed, with attention being concentrated on shell-focusing singularities at $r>0$. They find that although naked singularities can occur, this requires that the radial or tangential pressure must either be negative or equal in magnitude to the density.

Another model which has recently attracted some attention is the collapse of a fluid having only tangential pressure [@tp]. The analysis of the Einstein equations is considerably simpler than the case in which radial pressure is also present. Hence this is a useful system for studying the stability of dust naked singularities against the introduction of pressure. It has been found that while certain equations of state admit only black hole type singularities, other state equations admit naked singularities as well.

We conclude this brief discussion of fluids by commenting on the issue of whether fluids are a reasonable form of matter in so far as cosmic censorship studies are concerned. An objection sometimes raised against fluids is that they form singularities even in Minkowski spacetime, and hence the naked singularities that have been found do not have anything to do with general relativity. However, while some of the singularities, like the shell-crossings, and possibly the weak shell-focusings, have Minkowskian analogs, it is 