@Override
	public boolean equals(Object obj) {
		if (obj == null || !(obj instanceof Variable))
			return false;
		Variable other = (Variable)obj;
		if (this.getValue() == null && other.getValue() == null)
			return true;
		if (this.getValue() != null && other.getValue() != null)
			return this.getValue().equals(other.getValue());
		return false;
	}