@Override
	public boolean equals(Object o) {
		if (!(o instanceof OrderedHashSet<?>)) {
			return false;
		}

//		System.out.print("equals " + this + ", " + o+" = ");
		boolean same = elements!=null && elements.equals(((OrderedHashSet<?>)o).elements);
//		System.out.println(same);
		return same;
	}
Add a value to list; keep in hashtable for consistency also;
 Key is object itself.  Good for say asking if a certain string is in
 a list of strings.
runtime/Java/src/org/antlr/v4/runtime/misc/OrderedHashSet.java