Let a={ 1, 2, 3, 4, 5}

r={ (1,1), (1,2), (2,1), (2,2), (3,3), (4,4), (4,5), (5,4), (5,5) }

choose the partition of a that is defined by this equivalence relation r

{ {1,2}, {3}, {4,5} }

{ {1}, {2}, {3}, {4,5} }

{ {1,2}, {3, 4, 5} }

{ {1,2}, {3, 4}, {5} }