The language of sets
Set and structure language

We won't define what a set is. We'll simply set out a number of axioms and definitions, which enable us to manipulate relations and operations between sets. Nevertheless, it is essential to give meaning to these axioms, otherwise an intuitive use of sets would be impossible. In other words, we'll be giving a presentation of set theory that's often described (without being pejorative) as "naïve", and which aims to associate a symbolic construction with each relevant mental construction....