public int get(int i) {
		int n = intervals.size();
		int index = 0;
		for (int j = 0; j < n; j++) {
			Interval I = intervals.get(j);
			int a = I.a;
			int b = I.b;
			for (int v=a; v<=b; v++) {
				if ( index==i ) {
					return v;
				}
				index++;
			}
		}
		return -1;
	}
Get the ith element of ordered set.  Used only by RandomPhrase so
 don't bother to implement if you're not doing that for a new
 ANTLR code gen target.
runtime/Java/src/org/antlr/v4/runtime/misc/IntervalSet.java