It's used to indicate that something is an element of a set. So, in this example, we're using the symbol to indicate that the girl belongs to the set containing the boy and the girl. This …

Note: When discussing sets, there is auniversal set U involved, which contains all objects under consideration. For example: for A , the universal set might be the set of names of all fruits. for …

Definition Empty set, denoted by φ, is a set with no elements. Definition Two sets are called disjoint if, and only if, they have no elements in common. Problems Let A = {1, 3, 5} and B = …

If A and B are sets, we can create a new set named A B (spoken as “A minus B”) by starting with the set A and removing all of the objects from A that are also contained in the set B.

Think of a set as a box which contains (perhaps no) things. There is no repetition in a set, meaning each element must be unique. You could, for example, have variations on an …

Set Equivalence Two sets are equal if and only if they have the same elements. That is, if A and B are sets, then A and B are equal if and only if x(x A x B). We write A = B if A and B are equal …

Universal Sets and Complements The universal set is the set of all elements under discussion, such as all countries in the world, all students in a class, or all real numbers.