public class Expr {

	public static enum Operator {
		EQ, NE, GT, LT, LE, AND, OR, NOT
	}

	public static class Node {
		Operator	operator;
	}

	public static class CompareNode extends Node {
		String		id;
		String		value;
	}

	public static double SquareRoot (double x) { return 0.0; };
}