I am reading [this chapter](http://www.people.vcu.edu/%7Erhammack/BookOfProof/Relations.pdf) of the Book of Proof, and I'm stuck at the Exercise 10 of section 11.2. It is as follows.

> 
> Suppose $R$ and $S$ are two equivalence relations on a set $A$. Prove
> that $R \cap S$ is also an equivalence relation.
> 
> 
> 

Thanks for helps!