/// EquivalenceClasses<int> EC;
/// EC.unionSets(1, 2); // insert 1, 2 into the same set
/// EC.insert(4); EC.insert(5); // insert 4, 5 into own sets
/// EquivalenceClasses<int> EC;
/// EC.unionSets(1, 2); // insert 1, 2 into the same set
/// EC.insert(4); EC.insert(5); // insert 4, 5 into own sets