# Definition talk:Set of Sets

In $\mathsf{Pr} \infty \mathsf{fWiki}$ we like to allow for concepts to be accessible to those who have not studied so deeply as to understand the fundamentals, but have been introduced to the most naive of theories in which, for example, a "set" can consist of elements as concrete as physical objects. In such contexts it makes sense to introduce, in a semi-formal way, the concept of a set which contains nothing else but other sets.