Equivalence Relation/Examples/Books with Same Number of Pages

Example of Equivalence Relation
Let $P$ be the set of books.

Let $\sim$ be the relation on $P$ defined as:
 * $\forall \tuple {x, y} \in P \times P: x \sim y \iff \text { $x$ and $y$ have the same number of pages}$

Then $\sim$ is an equivalence relation.