(Review) Another Equivalence Relation
Let R = { (a,a), (b,b), (c,c), (d,d), (e,e) (a,b), (b,a),
(a,c), (c,a), (b,c), (c,b), (d,e), (e,d) }
R can be partitioned into two subsets, such that within each subset, all the elements are related in both directions.
The two subsets are called equivalence classes.