The first x stands for all possible numbers in a set. Common Symbols Used in Set Theory. In this book we will use capital letters for sets and lowercase letters for elements of sets.
X is an integer x 3 This is read as.
Symbols save time and space when writing. We can list each element or member of a set inside curly brackets like this. So in full formality the set would be written as. We will define a minimal amount of set-theoretical objects so that the concept of mathematical thinking can be understood.