In this post we will study the primitive elements of mathematics, which are fundamental to the elements of mathematics. This chapter is dedicated to set theory, however, let’s take it slowly. In each post we will talk a little about this complex and dense theory. In set theory it is necessary to have some primitive notions: primitive notions of set. primitive notions of membership, which we use the symbol belongs $\in$. Relevance In relevance, the relationship between sets can be established as follows: